SECURITY REPORT ,,Gold–silver ore mining of Certej ...apmtm-old.anpm.ro/files/ARPM TIMISOARA/Reglementari/DEVA GOLD - en/Security report...SECURITY REPORT ,,Gold–silver ore mining

SECURITY REPORT

,,Gold–silver ore mining of Certej perimeter”

Chapter 4

2010

Drawn up by S.C. OCON ECORISC S.R.L. Turda

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IV. Accidental risks identification and analysis and prevention methods

A. Detailed description of major accidents possible scenarios and their production

probability or the conditions in which they occur

In order to analyse the risks related to some potential accidents within the site, there

have been imagined a series of scenarios where hazardous substances are involved, with an

assessment of the causes, of the effects and with a qualitative assessment of production

probabilty, as well as of the severity of the consequences, for each of these scenarios, on

process operating phase.

I. Open Pit Mining Area -

a. Accidental explosions during handling of explosives. Probability that an explosive

mixture detonate by itself is reduced, Nitramon being sensitive to mechanical shocks. Under

certain conditions of storage and use, such as prolonged exposure to a heating source , that

one may accidentally detonate by increasing sensitivity to detonation, but these cases are

extremely rare.

Gravity of such an accident occurence is high enough, because it can result in

casualties.

b. Uncontrolled explosion of the explosive remained un-detonated after shooting has a

reduced probability. Even if it can produce missfire, these ones are detected on front check

that is always executed after shooting operation executed by the shotfirer. The probability not

to detect any missfire on front check is average. In case of their screening there is prepared a

liquidation plan of these ones, either by drilling of other holes near thereto that, by detonation

will produce also explosive destruction from these holes, or by applying loads over holes, in

case of secondary blasting of oversized material. On the other hand, the artfirers are

accordingly chosen on employment, when are following special courses that allow them

working with the explosive and they are periodically checked psychologically.

In case there still remain un-detonated holes exploding out of control, the produced

accident can be a severe one, resulting in personnel injury and material damages.

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c. Accidents (vibrations, noise, seismic waves), due to explosives use on rock

displacement, which may generate risks for human’s health and for construction area. Blasing

in the open pit is carried out on well-established schemes/patterns, with the explosive

quantities calculated accordingly for rock displacement, so that the generated seismic wave

will not affect the structures from the respective area.

The possibility that explosives detonation generate distructive effects on constructions

is reduced, but in the north eastern side of the open pit (nearest to the processing plant) there

is recommended that ovreburden operations/stripping operations be more carefully

controlled.

d. Working face collaps may occur in the following cases:

- Use of a too large explosive quantity. That is unlikely due to the fact that open pit

shootings are carried out on well-established schemes/patterns and according to the field

conditions.

- Existence of an undergound void under open pit bench. It is possible, due to totally

ignorance of the historical underground mining works at the site.

- The appearance of some massive failures or, of some friable intercalations that

determine ‚breaking’ of a much greater quantity of rock than the one initially provided. It has

a low probability, because the rocks from the massive was investigated and there are known

its geo-mechanical characteristics, and the surveyors and geologists will daily inspect the

working face, to detect the appearance of cracks/ fissures.

- Aquifer appearance or heavy rainfall on the mining area and failure to capture and

efficiently water discharge. It has a relatively low probability.

Probability of crumblings/landslides appearance is small on exploitation technology

compliance and of exploration works performing before strating-up a new working face and

through correct use of the blasting technologies.

Consequences can be moderated and consist of human casualties for the workers

from the working face, damage of the equipment from the open pit and possible fuel

accidental leakages on ground, damage of some pipelines or electrical cables along the

routes of which are situated on the affected area or nearby, access roads crumbling, thus

interrupring ore mining works until acces roads are repaird.

e. Car and work accidents produced during minining operations into the open pit

(material transport, drilling, blasting, manipulation, etc.) are specific for this type of activity

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and have an average probability, due to thorough organization of all these works, of the

permanent training of the executive staff and of the adequate protection means.

These accidents may produce more or less serious injury of one or more workers.

II. Processing plant

a. Totally distruction of plant installations through a terrorist attack, classical or

nuclear arms attack. Production probability is very low because the objective does not

present a strategic importance, triggering of such an attack usually involves a previous

conflict existance and thus the anticipation of such an event, which provides the necessary

time for installations shutdown eliminating toxic sources. Terrorist attack is an event with a

very low probability (even if greater that of an armed attack), but without being predicted will

have serious consequences. If after this accident contact is made with acid solutions

containing cyanides, there are generated large quantities of hydrocyanic acid which vanish

and reaches atmospheric air from plant area. Depending on weather conditions, the affected

area with lethal and dangerous concentrations of hydrogen cyanide can extend on long

distances, being able to produce intoxication and even death of the persons captured by the

toxic cloud without protection.

b. Serious damage of the storage tank of sodium cyanide solution, resulted in its entire

content leakage. It may occur in case of terrorist attack, tank wall cracking due to some very

big mechanical sollicitations or to some material defects. Production probability is small,

taking into consideration that the tank is placed in a closed chamber, but the tank is designed

and executed according to resistence and stability exigences for static, dynamic and seismic

loads. Even there is a whole sodium cyanide solution quantity leakage, its discharge is carried

out into the waterproof retention tray that is designed in order to provide the storage tank

integral collection. As well the retention tray is provided with a sump and with a submersible

pump that allow leakage re-pumping into the technological circuit. Such a leakage can

generate (especially in high temperature conditions) releases of hydrogen cyanide into the air

from the immediate proximity of the area affected by the leakage. As well there can be

sprayed the persons present within damage area.

c. Breakage of a container (Big-bag) with solid cyanide, resulted in discharge of its

contents. It is produced during internal transport and handling. It has a low probabililty

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because there will be implemented cyanide management specifical procedures both in terms

of the equipment used, as well as, in personnel training.

Breaking of a continer with solid cyanide is not serious, still it can affect the persons

located near and in some circumstances (rains, etc.) can lead to discharge relatively small

quantity of cyanide on the adjacent surface.

d. Breaking of a tank with hydrochloric acid solution, resulted in leakage of its

content. It can produce during transport of handling. It has an average probability because

handling is carried out with mechanical devices, and the material from which the tank is

manufactured is relatively fragile. The elapsed solution will be collected into the retention

basin/vat situated near the NaOH tank, that allows the operative neutralization if necessary.

The hydrochloric acid leakage conduct to corrosive HCl vapor released in the area,

possibly causing intoxication of the persons located near, but this kind of intoxications are

usually less serious, and the appearance of fog and the insightful smell warns regarding the

danger. By the way of placement of the storage and handling hydrochloric acid, the contact

with the solutions that contain cyanide is practically excluded.

e. Serious damage of one or of all the CIL leaching tanks, resulted in whole content

discharge. It can be produced in case of a terrorist attack, tank wall cracking due to some high

mechanical stress (earthquake, contractions/ important dilatations of the tank construction

material on abnormal low/ high temperatures). Production probability is reduced, taking into

consideration that tanks are designed and executed according to resistence and stability

demanding for static, dynamic and seismic loads. Discharge of the whole quantity of slurry

with cyanides contained into the leaching tank/ tanks conduct to its discharge into the

retention tank. If nothing is done or, masures of re-pumping or pumping flows are insufficient

for taking over the whole quantity of slurry discharged and as a consequence there will be

gradually flooded the concrete land surface nearby, finally being possible excess flow towards

open pit. Such a drain can generate (especially on high temperature weather conditions)

hydrogen cyanide releases into the air near the close nearby of the discharged liquid, but there

will not be reached toxic concentrations (due to alcalinity and to relative reduced

concentration of free cyanide).

f. Serious damage of the CIL thickener, resulted in its whole content discharge. It may

occur in case of a terrorist attack, tank wall cracking due to some very big mechanical stress

(earthquake, contractions/ important dilatations of tank construction material on abnormal

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low/ high temperatures, breaking of socket discharge). Production probability is small, taking

into consideration that it is designed and built according to resistence and stability demanding

for static, dynamic and seismic loads. Leaking cyanide slurry is collected into the retention

tank. Such a leaking can generate (especially on high temperature conditions) hydrogen

cyanide releases into the air from the close proximity of the drained liquid, but there will not

be reached toxic concentrations (due to alkalinity and to a free cyanide reduced

concentration). There can be sprayed and wounded the persons present within the damage

area.

g. Cyanidation installation severe damage DETOX 1 resulted in whole content

discharge of the reaction vessels. It may occur in case of a terrorist attack, tank wall cracking

due to some very big mechanical stress. Event occurence probability is low, taking into

consideration that the equipments are designed and built according to resistence and stability

requirements for static, dynamic and seismic loads.

Leaking of the whole cyanide slurry quantity contained into the reaction vessels

conduct to discharge into the retention tank. Such a discharge can generate (especially on

high temperature weather conditions) hydrogen cyanide releases into the air from the close

proximity of the discharged liquid, but there will not be reached toxic concentrations (due to

alkalinity and to very low concentration of free cyanide). There can be sprayed the persons

within the damage area.

h. Rich solution storage tank severe damages resulting in its whole content discharge.

It may occur in case of a terrorist attack, tank wall cracking due to some very big mechanical

stress. Event occurence probabilty is low, taking into consideration that, the road traffic area

is reduced, and the border around the platform does not allow cars acces to the tank, the tank

is designed according to resistence and stability requirements for static, dynamic and seismic

loads.

The leachage of the whole quantity of cyanide rich solution conduct to its discharge

into the retention tank. Such a leakage can generate (especially on high temperature weather

conditions) hydrogen cyanide releases into the air/atmosphere from the close proximity of the

discharged liquid, but there will not be reached toxic concentrations (due to alkalinity and to a

very reduced concentration of free cyanide). There can be sprayed the persons within the

damage area.

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i. Severe damage of the sodium hydroxide solution tank resulting of its whole content

discharge and /or, of the dissolution vessel. It may occur in case of a terrorist attack, tank wall

cracking due to some very stong mechanical stress.

The event occurrence probabilty is low, taking into consideration that the tank is

placed in a closed chamber and is designed according to resistence and stability requirements

for static, dynamic and seismic loads.

Even if the whole quantity of sodium hydroxide solution is leakaged it is desiged its

discharge into the waterproof retention tank in order to provide integral collection of the

storage tank and of the dissolution vessel. There can be sprayed the persons within the

damage area.

j. Severe damage of one or, of all Albion leaching tanks, resulting in whole content

discharge. It may occur in case of a terrorist attack, tank wall cracking due to some very big

mechanical stress (earthquake, important contractions/ dilatations of tank fabrication material

on abnormal low/ or high temperatures). The event occurrence probabilty is low, taking

into consideration that, tanks are designed and executed according to resistence and stability

requirements for static, dynamic and seismic loads and are placed inside the hall, therefore

less exposed.

Leackage of the whole quantity of slurry contained into the leaching tank/ tanks

conduct to its discharge into the retention tank. If nothing is done or, can not take action of re-

pumping or, pumping flowates are insufficient, there is possible that the retention volume of

the tank be insufficient for whole slurry quantity discharged and as a consequence the nearby

concrete land surface will be gradually flooded.

k. Severe damage of one or more flotation cells resulting in whole content

drainage/leackage. It may happen in case of a terrorist attack, walls cracking due to some high

mechanic stress. Event occurence probabilty is low, taking into consideration that they are

designed according to resistence and stability requirements for static, dynamic and seismic

loads and are placed within the hall, therefore less exposed. Leackage of the whole slurry

quantity conduct to its discharge into the retention tank. If nothing is done or can not take

action of re-pumping or, if pumping flowrates are insufficient, there is possible that tank

retention volume be insufficient for whole drained slurry quantity takeover and as a

consequence the nearby concrete land surface be flooded.

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l. Flotation tailings thickener severe damage, resulting in its whole content drainage. It

may occur in case of a terrorist attack, tank wall cracking due to some high mechanic stress.

Event occurence probabilty is low, taking into consideration that it is designed and build

according to resistence and stability requirements for static, dynamic and seismic loads.

Slurry drainage is collected into the retention tank, but there can eventually be hurt the

persons within damage area, therefore the consequences are minor.

m. Damages of the CuSO4 solution storage/ dosing tank resulting in its content

drainage. It may occur in case of a terrorist attack, tanks wall cracking due to some high

mechanic stress. Event occurence probabilty is low, taking into consideration that tanks

are designed and executed according to resistence and stability requirements for static,

dynamic and seismic loads. Consequences of such an incident are minor because the

tank is placed within the retention tank that provides integral collection of the drained

solution. Due to acidity of this solution, such drainage can generate minor hydrogen cyanide

releases into the air from the close proximity of the area affected by the drainage, if it comes

into contact with the slurry that contains cyanide. As well, there can be sprayed the persons

present within the damage area.

n. Severe damage of the process water storage tank, resulting in its whole content

drainage. It may occur in case of a terrorist attack, tank wall cracking due to some high

mechanic stress. Event occurence probabilty is low taking into consideration that, tank is

designed according to resistence and stability requirements for static, dynamic and seismic

loads. Process water drainage contained into the storage tank conduct to its drainage into the

retention tank from where is recycled into the technological circuit.

o. Damage of the acid water treatment plant decanter resulting in its whole content

drainage. It may occur in case of a terrorist attack or, of an armed one or due to some high

mechanical stress. Event occurence probabilty is low taking into consideration that decanter

is designed and built according to resistence and stability requirements for static, dynamic and

seismic loads. Drainage of the solution contained into the decanter conduct to its discharge

into the retention tank from where, it is recycled into the technological circuit. There can be

wounded only the persons present within damage area, therefore there are minor

consequences.

p. Severe damage of the lime slurry storage tank, resulting in its whole content

drainage. It may occur in case of a terrorist attack, tank wall cracking due to some high

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mechanical stress. Event occurence probabilty is low, taking into consideration that is

designed and built according to resistance and stability requirements for static, dynamic and

seismic loads.

Leackages will be collected into the retention tank. There can be sprayed the persons

present within damage area.

r. Accidents in reagent storage areas. Reagents storage is carried out in specially

designed storage rooms, provided with prevention and intervention systems, in original

packaging with rules compliance regarding incompatibilities, as such this kind of accidents

have a low probability of occurrence and the eventual consequences are minor.

s. GNU tank fires (extremely flammable product). They are possible in case of leakage

(escape) in contact to a fire source or spark or as a consequence of a previous explosion.

A specific feature of ignition possibility of gas leakages is the fact that these ones can

ignite from remote sources of ignition, even outside the target, within dispersion area of gas

found at concentrations over flammability limits.

In case of burning an under pressure leakage, the fire will be as a “JET FIRE ” (fire

type jet of fire’) for burning of some underpressure GNU pipeline and as a ‚FLASH FIRE’ for

burning of a gas leakage.

Fire jet direction will be depending on cracking place: horizontally, vertically or

oblique, jet power depending on the pressure of the supply source. The most dangerous are

the ones with horizontal and oblique jet, but they can be easily stopped and ‚turned back’

from the obstacles.

GNU storage tanks fire production has an average probability, GNU possible

leakages would be quickly seize by the detection apparatus and the ignition sources can be

presented only in case of some elementary work health and safety rules compliance.

ş. Explosions of the GNU tank can be produced through gas-air explosive mixtures,

CVE type (“Confined vapor cloud explosion”) and explosions through overpressurization

BLEVE type („boiling liquid expanding vapour explosion”).

CVE explosion can be produced in case of liquified petroleum gas leakages with

explosive athmosphere formation, in contact with a fire source or with a spark. Some mixture

explosion, within explosion limits, gas-air (liquified petroleum gas steam – air) within a

limited space (constrained) are CVE type “Confined vapor cloud explosion” steam

explosion within a closed space (constrained). BLEVE type explosion, explosion through a

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boiling liquid steam expansion, is typical on liquified gas as in case of luquified petroleum

gas, stored on a temperature superior to the boiling one and is accompanied by the ‚fireball’,

ball of fire, a burned area with an extremely high energy.

BLEVE type explosions on liquified petroleum gas can be produced through two

mechanisms:

- as a consequence of a sudden depressurization due to an important crack without

involvement into a fire, because of a corrosion or, of some high mechanical stress: cold

BLEVE’;

- as a consequence of a depressurization due to an important crack caused by

implication into a fire of installation parts (tanks, fuel truck, motor tank truck, pumps, pipeline

sections) that contain liquified petroleum gas and that are closed: ‚warm BLEVE’, when due

to warming up will occur material weakness and overpressurization enclosure, followed by

construction material breakage;

This kind of events have an average probability because:

- tank is periodically checked by ISCIR carrying out pressure tests on pressures

superior to the working ones and welding belts and wall thickness are checked.

- tank is positioned into the retention tank that does not allow approaching of some

tank equipments;

- area seismic risk is reduced.

- liquefied petroleum gas tank is positioned outdoors, space constraint is low and is

due to the surrounding buildings.

In case of explosions, personnel and goods within the area will be affected, through

the pressure produced by the explosion (shockwave), thorugh the energy eliberated (fire ball,

ball of fire) or through mechanical impact of debris thrown by explosion blast.

t. Damages on oxygen plant and distribution installation, that consist of explosions of

the buffer vessels and/or of transportation routes being under pressure, can occur only on

conditions of lack or failure of safety valves and these are events with a low probability due

to special equipments that form it, to design, execution and special control according to ISCIR

requirements.

This kind of damages can cause serious injuries, but only to the persons within the

damage area.

ţ) Explosion of an oxygen cryogenic tank can occur due to tank over-pressurization

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above the breaking limit of this. Pressure increase can take place as a consequence of

cryogenic isolation loss resulting after air penetration within the isolation space, where there

is vacuum (loss of vacuum).

The increase of one tank pressure above the adjusted value of the safety valves will

trigger. If discharge through valves will not be able to provide pressure maintenance into the

tank, breaking flange breakage with which tank is provided, can occur. In most serious cases,

when safety systems (safety valves, rupture disk) does not function correctly, sudden

depressurization of liquid oxygen tanks will be able to produce BLEVE explosion (without

‚fire ball’) of these ones.

Oxygen tank explosion is unlikely because:

- any vacuum loss and tank warming up is quickly seized through exterior surface

cooling (ice appearance on the tank) that allows taking of operational measures and

ultimately, tank discharge;

- vacuum loss usually takes place through reduced cracks (small leaks) and thus

warming up takes place slowly, while there is time for intervention;

- tanks involvement into fire is possible only in case of storage of some combustible

substances in the area, that is forbidden. Even in case of tanks involvement into a fire due to

cryogenic isolation, at least for a while their content is protected, only exterior equipment

being directly exposed (pipeline, valves, exterior jacket);

- safety valves and rupture flange sizing is so made that to avoid tanks explosion;

- both the tank itself, as well as the related equipment are designed and built taking

into consideration temperature and pressure weather conditions that they are working in;

- tanks and equipments are authorized and periodically checked according to ISCIR

requirements;

In case of the oxygen tank, an explosion will affect personnel and goods through the

pressure produced by the explosion (shockwave), or through mechanic impact with debris

thrown through explosion blast. Release of some large quantities of oxygen will lead to

oxygen enrichment of the area near tank, being able to cause fire or explosion of the organic

substances eventually present. As well, explosion will cause liquefied oxygen drainage, un-

vaporized within explosion.

u. Cyanide solution vehicular systems damages (pipeline, fittings, pumps) resulting in

drainages, can occur along all the operation period and have an average occurrence

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probability (slightly higher on pumps starting-up and within areas provided with sealing

systems – glands, flanges).

Such a drain can generate (especially on high temperature weather conditions) minor

hydrogen cyanide releases into the air from damage close proximity, but there will not be

reached toxic concentrations (due to high alkalinity and reduced quantities). As well, there

can be sprayed the persons present within damage area.

v. Damages on hydrochloric acid solution circulation systems (pipeline, fittings,

pumps) resulted in drainages, can occur during the whole operation period and have an

average occurrence probability (slightly higher on pumps starting-up and within areas

provided with sealing systems – glands, flanges).

Hydrochloric acid drainage conduct to corrosive hydrochloric acid vapours release

into the area, but for this type of damage, the drained quantities are very low, so possible

intoxication of the persons located nearby is very unlikely, and these intoxications are usually

less serious, with fog appearance and insightful smell warning on danger. More serious can be

eventually acid contact with cyanides eventually existing on the surface affected by the

drainage, when there takes place hydrogen cyanide releases (in very small quantities), with

possible damage of the persons nearby.

x. Damages on solutions/ cyanide content suspensions circulating systems (pipeline,

fittings, pumps) resulting in drainages, can occur during whole operation period and have an


provided with sealing systems – glands, flanges).

These drainages consisted in relatively small quantities of material that is produced

only in protected areas of waterproof surfaces (with the exception of pipes from plant

inlet/outlet scaffold) with their capture and routing towards emergency catchment. Due to

cyanide relatively low content and to high pH, hydrogen cyanide releases are practically

excluded (with the exception of accidental contact with hydrochloric acid or with other acid

solutions). Due to high alkalinity and to cyanide level, the spraying of operators within

emergency area can have rather serious consequences.

y. Damages of sodium hydroxide solution transportation systems (pipeline, fittings,

pumps) resulting in drainages, can occur during the whole operation period and have an


provided with sealing systems – glands, flanges). The NaOH solution drainage on the floor

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does not present any risk, but the risk of spraying the possible operators within the area, their

possible injury being able to be rather serious if the corrosive drops reaches the eyes and no

washing steps and first aid are immediately taken.

z. Damages of the transportation systems and/or tailings slurry transportation systems

(pipeline, fittings, pumps) resulting in drainages, can occur during the whole operation period

and have an average occurrence probability (slightly higher on pumps starting-up and

within areas provided with sealing systems – glands, flanges). These drainages represent only

a very low danger, being in a low quantity that is collected on concrete surfaces and

conducted towards the emergency tank (with the exception of pipes from plant inlet/ outlet

scaffolds). Possible spraying of the operators from emergency area can cause just minor

effects.

w. Operation errors and/or failures of measuring and control systems resulting in

slurry pH decrease into the leaching tanks, into the thickener and/or DETOX plant. There are

less probable due to automatic control doubled by periodical execution of physical-chemical

parameters analyze of slurry within the lab and of continuous monitoring of hydrogen cyanide

level into the air.

The effects of this kind of damages can be seriously enough due to increase of

hydrogen cyanide level into the air beyond leaching tanks (especially on high temperature

weather conditions) with impairing the operators within the hall. The pH decrease can occur

very slow (even in total absence of lime milk dosing) due to very big volume of liquid into

each tank, reaching some dangerous pH values and taking place a few hours in the first

leaching tank, while damage is practically impossible to be traced and repaired, hence

possible effects have an average gravity and a short period of time.

aa. Operation errors and/or failures of waste water treatment systems resulting in

overcoming of the maximum admissible pollutant levels into the waste waters discharged into

the emissaries. They have a reduced probability of occurrence due to some permanent and

automate control of treated waters physical-chemical parameters. The improper treatment of

the water discharged can generate minor and short term effects that consist of downstream

surface waters quality affecting. The most serious is the situation when the damage is

produced at the CIL TMF clarified water neutralization plant, but in this case immediate

interruption is possible of the pumping towards the station, and thus possible negative effects

will be on short term.

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ab. Operation errors and/ or failures on DETOX 1 neutralization plant. They have a

low probability of occurrence due to continue and periodical control (with redox sensors and

through lab analysis) of the tailings slurry physical-chemical parameters before discharge into

the cyanide tailings pond.

The improper treatment of the tailings slurry discharged (with a high cyanide content)

cannot generate serious damages due to dilution of a relatively reduced quantity of liquid into

the very large volume of water existing into the pond.

ac. Operating errors, resulting in insufficient washing of active carbon before acid

washing up. They have an average probability of occurrence due to lack of an automatic

control of the cyanide remnant content onto active carbon subject to acid washing.

The insufficient washing of active carbon can conduct to small quantities of

hydrocyanic acid (HCN) release when in contact with the washing acid, but this phenomenon

occurs within the washing column that is provided with ventilation, with a gas dispersion

stack.

ad. Damages of supply system and of power distribution, consisting in short-circuits

and/or overheating followed by conductors ignition or even that of transformers. These are

events with a low probability of occurrence, design and system accomplishment being

achieved according to safety standards imposed by field requirements, the used materials are a

good quality ones, there are safety and control automate systems that provide de-energizing

(partial or total) immediately there produces a system operation normal parameters disorder.

The only event of this kind that can have serious consequences consisting of important

material damages is transformation stations fire, when there can also take place intervention

personnel injury.

ae. Interruption of electricity supply from company exterior reasons is an event that

has a low occurrence probability, taking place only in special situations occurred within

national energy system. Unplanned interruption of electrical power can have pretty serious

consequences, but usually on short term. In case of a longer term interruption during very low

temperature weather conditions periods of time, this can lead to freezing of some solutions

along vehicular routes that increases some damages production probability on installations re-

starting-up.

af. Working accidents produced within maintenance and reparations or intervention

works have a reduced probability of occurrence, due to thorough organization of all of

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these works that are executed under direct surveillance of the specialized technical personnel,

of execution personnel permanent training and of endowment with individual protection

means and with tools and appropriate and quality working devices.

Working accidents produced during maintenance and reparations or special

intervention works can produce hurting/injury or, less or more severe intoxication of more

workers.

III. Explosive magazine

a. Explosion within storage yard. Because within explosive storage yard there are

provided guard and security specific conditions, explosives handling is carried out according

to some special proceedings and only by authorized personnel, the probability of occurrence

of such kind of explosion is very low.

Possible explosion of the whole explosive material quantity existing within the storage

yard will be extremely strong, producing injury or even death of the nearby persons but

without affecting buildings or persons situated outside storage yard site.

b. Vehicle explosion that carries out explosive transport. It may occur during transport

to the storage yard, during un-loading/ loading operations or during transport from the storage

yard to the open pit. Probability of occurrence of this kind of accident is low because

transport speed within enclosure is regulated and the vehicles that carry out internal transports

are specially destined to this scope.

Consequences can be severe because the involved quantity is rather great and such

kind of accident will certainly produce injury or even death of the persons situated nearby

and will affect built structures and equipment possibly situated on transport route, close to the

place where deflagration takes place.

c) Ammonium nitrate (NA) stored into the warehouse (excepting an air attack or a

terrorist attack situation) can take place following a chain of human errors that lead to

ammonium nitrate detonation from the storage yard: breaking of more ammonium nitrate

bags, leakage of a liquid fuel on ammonium nitrate, fire with open flame within the area

where there is mixture of nitrate with liquid fuel of production of strong shockwaves,

explosive materials explosion from the storage yard or situated on the lifting platform.

Ammonium nitrate explosion may occur during transport, on the road or within the career,

existing a prior background contamination of nitrate with organic substances or as a

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consequence of combustible substances existence within handling space. Possible

contamination sources are the combustibles used by transport vehicles that use gas as a fuel.

In case of some failures with loss occurrence, of fuel leakage there are created conditions

favourable for fires.

Ammonium nitrate explosion occurrence within the storage yard has an average

probability, due to storage conditions and to operation requirements within storage yard.

Explosion destructive effects are due to overpressure existence on shock wave front, flow

of thermal radiation produced by explosion for persons exposed and forming of a

contained cloud with nitrate oxides.

IV. Flotation tailings pond

a. Flotation TMF total failure can be produced in case of a terrorist attack or, of an

attack with classical or nuclear weapons. The occurrence probability is very low for the

armed attack because the objective does not present strategic importance, and triggering of

such an attack usually assumes the existence of a previous conflict and thus anticipation of

such an event, that provides the necessary time for stopping activity and taking measures to

reduce to a minimum the impounded water quantity. Terrorist attack remains an event with a

very low probability (even though greater than of an armed attack), but cannot be anticipated.

Such an accident can have severe consequences consisting in forming a flood wave

formed from the water discharged from the tailings pond together with the tailings slurry

involved that can significantly affect important land surfaces and downstream water courses

as concern their quality, to which are added important material damages and possible

downstream population health impacts.

b. extreme natural events, such as extremely strong earthquakes and/or exceptional

precipitations can generate dam breakthrough forming.

The potential mechanisms responsible for tailings embankment failure are:

- Seismic events. Seismic activity is reduced within the area and at TMF design there

were calculated the fully covering parameters for seismic risk that characterizes the zone in

question. Design seismic parameters adopted in case of TMF equals or overcome the safety

factor 1.1, considered sufficient, according to national and European requirements for this

kind of design.

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- Overloading. Project envisages dam construction in stages, so that safety parameters

be provided (minimum freeboard and beach) that allow existence of a capacity reserve in case

of exceptional storm events calculated at 1/1000 probability of occurrence.

- Structural deficiencies, foundation failure. Foundation achievement way and dam

designed structure provides a very good stability, making extremely unlikely a damage due to

some foundation failure or to a structural deficiency. From the safety point of view, the

adopted construction solution (rockfill dam) is superior to techniques applied in most of

world’s tailings management facilities and land structure within the TMF’s site area was

investigated through detailed geotechnical studies. A special attention is paid to the

construction of the diversion and drainage gallery that crosses the embankment.

- Suffusion. Taking into consideration the constructive features of the dam (especially

rock-fills use), the occurrence of this phenomenon can be produced only in case of faulty

construction.

- Erosion and slope instability. Erosion phenomenon can take place under water

precipitations/ torrent influence that are falling/ running off on dam slopes. The embankment

being a rockfill construction, with fragments of large dimensions, the erosive influence of

precipitations/ torrent run off waters is insignificant.

The probability of occurrence of such an accident is very reduced taking into

consideration that the dam is included into the second class of importance and the project was

designed taking into consideration the safety conditions imposed by the norms in force and by

the engineering practice.

Consequences of such kind of an accident will consist of seepages of water and tailing

with the impact on a significant land surface and impact on the quality of water of

downstream emissaries; in addition a series of material damages can occur and eventual the

impact against the human’s health downstream. All these consequences are as severe as the

dimension of the dam’s breakthrough is larger.

c. Damages resulting in discharges over dam crest/dam overtopping (through

emergency channels) have a very low probability of occurrence taking into consideration

that, the project provides a storage capacity of water within the pond equivalent to maximum

probable precipitation calculated for 0.1% probability of occurrence. These can take place

only in conditions of systematic non-compliance of the exploitation parameters on long term

(the minimum pond beach and the freeboard) and/ or, the occurrence of damages on drainage

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and discharge systems of the clarified water discharged from the tailings pond during special

meteorological situations (heavy rainfall).

These damages have consequences with an extremely reduced gravity, because the

water seepages contain a relative low level of hazardous substances, which could impact the

quality of downstream waters.

d. Cracking and fissuring of the diversion and discharge gallery resulting in

infiltrations of clarified pond water into the gallery have a low probability of occurrence if

the requirements of the execution project are complied.

Consequences consist of contamination of downstream waters with heavy metals and

cyanides and significant degradation of the surface water quality. Because the infiltration

flow-rates and pollutant contents are relatively reduced, the gravity of such an accident can

be considered as being moderate.

e. Clogging of diversion and drainage gallery resulting in the impossibility of collected

water discharge is an event with a reduced probability of occurrence if the requirements of

the execution project are not observed.

Consequences can be serious and consist of pond retention capacity reduction, all

upstream run off waters being retained within the pond. More serious consequences has the

clogging produced even within the dam area followed by the gallery cracking/fissuring and

exfiltration of the collected waters, when a progressive erosion can take place into the dam

body and finally its failure, with previously mentioned consequences.

f. Breaking or failure of slurry distribution pipelines are events with an average

probability of occurrence due to erosion, and this probability increases under very low

temperature conditions.

This kind of accidents has minor effects and in general on short term; they produce

tailings discharges/leakages on the adjacent areas and still within the pond.

g. Severe damages on pumping system of the clarified waters collected from the pond

towards the processing plant consisting in pump failures, electrical power interruption,

breaking or tearing of recycling duct, all have an average probability of occurrence.

They produce effects on short term and the gravity is mean in conditions when

exceptional precipitations occur, resulting in pond level increase beyond the safety limit of

dam operation.

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h. Electrical power supply and distribution system damages are events with low

probability of occurrence, the system designed and the compliance being achieved

according to the safety standards imposed by the field requirements.

Electrical power supply unplanned interruption can have moderate consequences

consisting of short term interruption of clarified water pumping (power generators fuelled

with Diesel motor provide necessary emergency power supply).

i. Working accidents produced during maintenance, reparation or intervention works

have a low probability of occurrence, due to careful organization of all of these works that

are carried out under direct surveillance of specialised technical personnel and after

permanent training of the execution personnel and with individual protection means

endowment and with tools and appropriate and quality working devices.

Working accidents produced during maintenance and reparations works can produce

injury on one or more workers and this can be considered as being an event with minor

consequences.

V. CIL pond

a. Dam total failure can occur in case of a terrorist attack or, of an attack with classical

or nuclear weapons. The probability of occurrence is very low for the armed attack because

the objective does not present any strategically importance, and triggering of such an attack

usually assumes some previous conflict existence and thus anticipation of such an event that

provides the necessary time for activity stopping and taking measures in order to reduce to a

minimum the impounded water quantity. Terrorist attack remains an event with a very low

probability of occurrence (even if greater than that of an armed attack), but cannot be

anticipated.

Such kind of an accident can have only minor consequences consisting of seepages

that will be collected into the retention area located between CIL TMF and flotation TMF

upstream dyke. In some exceptional situations seepages can pass through the upstream dyke

and will be taken over within the flotation TMF. .

b. dam breakthrough can have as causes extreme natural phenomenon, such as

extremely strong earthquakes and/ or exceptional precipitations. Potential mechanisms of dam

failure are:

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- Seismic events. Seismic activity is very low within the area and on tailings dam

facility design there were taken into consideration the calculation of fully covering parameters

for seismic risk that characterizes the area in question.

- Overloading. Project takes into consideration dam construction in stages, so that

safety parameters be provided (minimum freeboard and beach) that allow the existence of a

storage capacity in case of exceptional precipitations calculated 1/1000 probability of

occurrence.

- Structural defects, foundation failure. The design of dam foundation and

structure provide a very good stability, making extremely unlikely a damage due to

some foundation or structural failures. From safety point of view, the adopted constructive

solution (rockfill dam) is a superior techniques applied in most worldwide TMFs and the

structure of the site area was studied through detailed geotechnical studies. A special attention

will be paid to the execution of diversion and drainage gallery that under-cross the dam. From

the safety point of view, the adopted constructive solution (rockfill dam) is superior to

techniques applied on most of worldwide decanting ponds and land structure within dam site

area was studied through detailed geotechnical studies. A special attention will be paid to the

execution of deviation and drainage gallery that crosses the dam.

- Suffusion. Taking into consideration the constructive features of the dam (mainly

rockfill use), the occurrence of this phenomenon can be produced only in case of some faulty

construction.

- Erosion and slope instability. Erosion phenomenon can manifest under the influence

of precipitations/ torrent waters that fall/ drain towards the dam slope. Dam being built from

rockfill, with large dimensions fragments, erosion influence of precipitations/ torrent waters is

insignificant.

Probability of occurrence of such an accident is very low taking into consideration

that the tailings dam is included within the second class of importance and the project is

complying with the requirements in force and the engineering practice.

Consequences of such an accident will consist of water and tailings seepages that will

be collected into the retention basin located between the CIL TMF and the Flotation TMF

upstream dyke and in the worst scenario into the flotation TMF.

c. Damages resulted in dam overtopping (through emergency channels) have very low

probability of occurrence taking into consideration the fact that, through the project there is

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provided a storage capacity of the water within the pond for the maximum probable

precipitation calculated at 0.1% safety factor . They can take place only in terms of systematic

non-compliance and on long term of exploitation parameters (minimum beach and freeboard)

and/ or occurrence of some long term emergencies on the drainage system and on pond

decanted water discharge system correlated to special meteorological conditions (heavy

precipitations).

These emergencies can have consequences of a relatively low gravity, because

seepage/exfiltration waters will be collected within the retention area located between CIL

tailings pond and upstream dyke of the flotation TM or, in the worst case into the flotation

TMF.

d. Cracking of the diversion and drainage gallery resulted in infiltration of waters

drained from the pond into gallery has a low probability of occurrence if the requirements of

the execution project are respected.

Consequences consist of heavy metal and cyanide contamination of the waters

discharged into the emissaries and thus significant degradation of downstream surface water

quality. The gravity of such an accident can be considered moderate as the infiltration flow-

rates and pollutants are relatively reduced.

e. Diversion and drainage gallery clogging resulting in the impossibility of collected

water discharge is an event with low probability of occurrence if this complies with the

requirements of the execution project.

Consequences consisted of reduction of the pond retention capacity, all upstream run

off water being retained within the pond. More serious consequences has the clogging

produced exactly on dam area, followed by gallery cracking and collected waters ex-

filtration, when there can take place gradual erosion within dam body and finally its failure,

with the previously mentioned consequences.

f. Tailings slurry distribution pipes cracking/fissuring are events with an average

probability of occurrence due to erosion, but in conditions of some very low temperatures

and severe weather conditions this possibility increases.

This kind of accident has minor effects and generally on short term, producing tailings

slurry discharges on adjacent areas and continuing into the pond

g. Severe emergencies on pumping system of clarified waters collected from the pond

towards the processing plant and on seepage pumping station consisting in pumps failures,

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electrical power interruption, breaking or tearing of ducts, all have an moderate probability

of occurrence.

They produce short term effects and the gravity is reduced if they are produced

simultaneously with exceptional precipitations.

h. Hydrogen cyanide toxic aerosol forming on lake surface is permanently produced,

the quantity released into the atmosphere depending on pumped solution physical-chemical

characteristics and existent on the pond, as well as on meteorological weather conditions.

In periods of strong sun exposure and high temperature, the hydrogen cyanide

quantity released to the pond surface increases, but if pH keeps within normal technological

limits, the hydrogen cyanide concentration from atmospheric air does not reach dangerous

concentrations, not even on lake- surface. As such the consequences are insignificant (details

regarding hydrogen cyanide dispersion formed on CIL TMF surface were presented in

subchapter 4.2).

i. Damages at the electrical power supply and distribution system are events with a

low probability of occurrence, the system and execution designed being carried out according

to the safety standards imposed by field regulations.

Unplanned interruption of electrical power supply can have moderate consequences

consisting of decanted water pumping interruption and of exfiltrations from dam body for a

short period of time (electrical power generators fuelled with Diesel motor provide necessary

damage power supply).

j. Work accidents produced during maintenance and repair or intervention works are

unlikely, due to careful organization of all these works performed under the direct

supervision of specialized technical staff, continuous staff training and endowment with

personal protection means and with adequate and quality working tools and devices.

Work accidents produced during maintenance and repair or special intervention works

may cause injury to one or more workers and can be considered as events with minor

consequences.

VI. Pipeline corridor hydro-transportation

a. Hydro-transportation pipeline cracking/ breaking of flotation tailings slurry from

due to wear or erosion (especially within sensitive areas – elbows, flanges, compensators,

valves) have a moderate probability of occurrence. Use of some appropriate thickness

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pipeline, permanent inspections and its regular technical expertise substantially reduces this

probability.

This kind of damages determines hazardous material leakages and on small

quantities, having an impact on small land areas, adjacent to the corridor, thus the effects are

insignificant.

b. Cracking / breaking of the Flotation TMF clarified water pipeline to the processing

plant is unlikely to occur due to lack of suspension to generate erosion. However there is a

slightly risk higher in the flexible area (between the floating barge and pipe fixed to the

ground) because of possible rapid and large fluctuations of free fluid level into the pond.

Such failures produce non-hazardous liquid leakages in small amounts with impact on

small land areas, adjacent to the corridor, so the effects are insignificant.

c. Cracking / breaking of slurry hydro-transport pipeline from the CIL process due to

wear or erosion (especially in sensitive areas - elbows, flanges, compensators and valves)

have an average probability of occurrence. Use of appropriate thickness pipeline,

permanent inspections and compliance with its regular technical expertise substantially

reduces this probability.

This kind of damages produce leakages of hazardous material but in small quantities,

with the effect on reduced land areas located adjacent to the corridor, so the effects are

insignificant.

d. Circulation pipeline cracking / breaking of decanted water from the CIL pond to

the processing plant is unlikely to be produced due to lack of solids to generate erosion.

However there is a slightly higher risk in the flexible area (between floating barge and

pipeline fixed to the ground) because of some possible rapid and large fluctuations of free

fluid level into the pond.

Such failures generate hazardous liquid leakages but in small quantities, affecting some

reduced land surfaces, adjacent to the corridor, so the effects are insignificant.

e. Work accidents produced during maintenance and repair or intervention works on

pipelines or related facilities have an average probability of occurence, due to careful

organization of all of these works that are carried out under direct surveillance of specialized

technical staff, of ongoing training of personnel and of endowment with individual protection

means and with proper and quality working tools and devices.

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Work accidents can cause injuries to one or more workers and can be considered as

events with minor consequences.

VII. Transport activity

a. Traffic and work accidents produced during internal transportation of ore from the

open pit to processing plant as well as, of waste rocks to the waste dumps, have an average

probability of occurrence, due to careful organization of all of these works, roads

arrangement plan, permanent training of the staff and of the endowment with appropriate

equipments and working and protection means.

These accidents can cause more or less severe injuries to one or more workers and

possible material damages, so the consequences may be considered insignificant.

b. Fires, explosions and leakages of hazardous substances associated with accidents

occurred during the outside transportation can take place on equipment failure, human errors,

special weather conditions, traffic conditions etc. The occurrence probability is low given the

security measures adopted by the company (including the use of certified and experienced

carriers).

Event severity depends on the place of occurrence, on nature and quantity of

transported substance but taking into consideration that all dangerous substances are

transported by means of transport vehicles and specially designed packaging, the

consequences can be considered moderate.

Intervention measures provided for accidents help to reduce the effects of discharges

of fuels / chemicals. Vulnerable points along the haulage route are represented by the urban

areas, proximity of re-fuelling stations, water courses.

B. Assessment of the consequences and amplitude of the identified major accidents

1. Quality assessment. Risk assessment matrix

To assess the magnitude and gravity of the consequences of the site specific major

accidents, there was a qualitative assessment of risk associated with the above scenarios.

Qualitative analysis has as main objective to establish a list of possible hazards, makes

it possible hierarchy of events in order of risk and presents the first step in carrying out risk

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analysis methodology. Qualitative risk assessment is done by calculating the level of risk as

the product between the level of security and that of probability of event analysis.

a. Qualitative measure of consequences is carried out through framing within five

gravity levels, that have the following significance

1. Insignificant

• For people (population): insignificant injuries

• Emissions: without emissions;

• Ecosystems: Some minor unfavourable effects on few species or ecosystem parts, on

short term and reversible

• Socio-political: Insignificant social effects with no reason of concern.

2. Minor

• For people (population): first aid is necessary;

• Emissions: emissions within objective premises immediately detained;

• Ecosystems: insignificant damages, rapid and reversible for few species or parts of

the ecosystem, animals forced to leave the usual habitat, plants are unfit to develop after all

natural rules, air quality creates a local discomfort, water pollution exceeds fund limit for a

short period of time;

• Socio-political: Social effects are few reasons for community concern.

3. Moderate

• For people (population): there are necessary medical treatments;

• Economical: production capacity reduction;

• Emissions: emissions within objective premises withheld with external help;

• Ecosystems: temporary and reversible damages, damages on habitats and animals

population migration, plants unfit to survive, air quality affected by the compounds with a

potential risk for long term health, possible damages for aquatic life, ground limited

contaminations that can be quickly corrected;

• Socio-political: Social effects with moderate reasons of concern for community.

4. Major

• For people (population): serious injuries;

• Economical: production activity interruption;

• Emissions: emissions outside the site without harmful effects;

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• Ecosystems: death of some animals, large scale injuries, damages on local species

and destruction of extended habitats, air quality imposes ‚safety refugees’ or evacuation

decision, ground remedy is possible only through long term programmes;

• Socio-political: Social effects with serious concern reasons for community

5. Catastrophic

• For people (population): death;

• Economical aspect: production activity stop;

• Emissions: toxic emissions outside the site with harmful effects;

• Ecosystems: death of animals in a large number, flora species destruction, air quality

imposes evacuation, permanent contamination on ground extended areas;

• Socio-political: Special effects with very serious reasons of concern.

b. Occurrence probability measure is accomplished also through framing within five

levels that have the following significance:

1. Rare (unlikely) – it produces only in exceptional conditions;

2. Unlikely could happen sometime;

3. Possible – it may happen sometime;

4. Probable – it may happen in many situations;

5. Almost certain – happens in most of the situations.

Using information obtained from analysis, risk is placed in a matrix of the following

form (table 4.1):

Table 4.1. Risk assessment matrix

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Consequences

Insignificant Minor Moderate Major Catastrophic

1 2 3 4 5

Improbably 1 1 2 3 4 5

Isolated 2 2 4 6 8 10

Occasionally 3 3 6 9 12 15

Probably 4 4 8 12 16 20

Pro

bab

ilit

y

Frequent 5 5 10 15 20 25

Risk level Definition Actions that should be performed

1 – 3 Very low risk

4 – 6 Low risk The actions are managed through regular, routine procedures,

7 – 12 Moderate risk The actions are taken through specific standard procedures, with

the involvement of the managing team at the work site.

13 – 19 High risk

Prompt actions, taken as soon as possible as permitted by the

regular management system, with the implication of the top

management

20 – 25 Extreme risk Being an emergency situation, immediate actions are required to

be taken and all the available resources will be used

For risk assessment related to the activity carried out within the emplacement, we

proceeded to the allocation of numerical values for each level of severity of consequences and

probability of occurrence of the predicted imagined accident, risk associated to each scenario

being represented by the product of the two values assigned. To determine the associated

levels of probability and severity there is taken into account the potential impact and

prevention measures provided.

For a more suggestive presentation of the findings resulting from accidental risk

analysis specific activity within the site, the risk management matrix is presented below, made

on the possible accidents scenarios described above (Table 4.2).

Table no. 4.2 Risk quantification matrix

Crt.

No. Danger Probability Gravity Risk

I. Open pit

a Explosives accidental explosions 2 4 8

b Un-detonate explosive; uncontrolled explosion 2 3 6

c Vibrations due to explosives 4 1 4

d Subsidence of work face 2 3 6

e Road and work accidents 3 2 6

II. Processing plant

a Total destruction of plant installations 1 5 5

b Cyanide storage tank damage 2 2 4

c One solid cyanide tank breaking 2 2 4

d One hydrochloric acid solution tank breakage 3 1 3

e CIL leaching tanks damage 2 2 4

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f CIL thickener damage 2 2 4

g DETOX 1 installation damage 2 2 4

h Rich solution storage tank damage 2 2 4

i NaOH storage tank damage 2 1 2

j Albion leaching tanks damage 2 2 4

k Flotation cells damage 2 1 2

l Flotation tailings thickener damage 2 1 2

m CuSO4 solution tank damage 2 2 4

n Process water tank damage 2 2 4

o Acid water treatment plant damage 2 2 4

p Lime slurry tank damage 2 1 2

r Accidents within the reagents storage 1 2 2

s Liquefied petroleum gas tank fires 2 3 6

ş Liquefied petroleum gas tank explosions 2 4 8

t Oxygen plant damages 2 3 6

ţ Cryogenic oxygen tank explosion 2 4 8

u Cyanide solution transportation systems damages 2 2 4

v Hydrochloric acid solution vehicular systems damages 2 1 2

x Cyanide solutions/ suspensions transportation systems

damages 3 2 6

y Sodium hydroxide solution transportation systems

damages 2 2 4

z Damages on tailing slurry transportation and/or

preparation systems 3 1 3

w Operation errors and/or failures on measurement and

control systems 2 2 4

aa Operation errors and/ or wastewater treatment plant

failures 2 2 6

ab Operation errors and/or failures on DETOX 1

neutralization plant 2 2 4

ac Operation errors, resulted in insufficient washing of

active carbon before acid washing. 3 1 3

ad Electrical power supply and distribution system damages 2 2 4

ae Electrical power supply interruption 2 2 4

af Work accidents 3 2 6

III. Explosive storage magazine

a Explosion within storage magazine 1 4 4

b Vehicle explosion that carries out transport of explosives 2 4 8

c Ammonium nitrate explosion 2 3 6

IV. Flotation TMF

a Dam total failure 1 4 4

b Dam breaking through 1 4 4

c Dam overtopping 1 3 3

d Diversion and drainage gallery cracking 2 2 4

e Diversion and drainage gallery clogging 2 3 6

f Slurry distribution pipelines breakage or cracking 3 1 3

g Serious damages on clarified water pumping system 3 2 6

h Electrical power supply and distribution system damages 2 2 4

i Work accidents 3 2 6

V. CIL TMF

a Dam total breakage 1 3 3

b Dam breaking through 1 2 2

c Dam overtopping 1 2 2

d Diversion and drainage gallery cracking 2 3 6

e Diversion and drainage gallery clogging 2 2 4

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f Slurry distribution pipelines breakage or cracking 3 2 6

g Clarified water pumping system serious damages 2 2 4

h Hydrocyanic acid toxic aerosol formation on pond

surface 4 1 4

i Electrical power supply and distribution system damages 2 2 4

j Work accidents 3 2 6

VI. Hydro-transportation pipeline corridors

a Flotation tailings slurry hydro-transport pipeline cracking/

breakage 3 1 3

b Flotation TMF clarified water recycle pipeline cracking/

breaking 2 1 2

c CIL tailings slurry hydro-transportation pipeline cracking/

breaking 3 2 6

d CIL TMF clarified water recycle pipeline cracking/

breaking 2 2 4

e Work accidents 3 2 6

VII. Transport activity

a Traffic and work accidents produced during internal

transportation 3 2 6

b Fires, explosions and/or dangerous substances associated with external transport and traffic accidents

2 3 6

In figure 4.3. there are centrally presented risk qualitative analysis results. In grid

bounded areas are mentioned security area index and the scenario corresponding number:

Figure 4.3 Risk qualitative analyse – Operating phase

Frequently

Probable Ic, Vh,

Occasional IId-z-ac, IVf,

VIa

Ie, IIx-af, IVg-i, Vf-j,

VIc-e, VIIa

Isolated IIi-k-l-p-v, VIb

IIb-c-e-f-g-h-j-m-n-o-

u-y-w-aa-ab-ad-ae,

IVd-h, Ve-g-i, VId,

Ib-d,IIs-t,

IIIc, IVe, Vd,

VIIb,

Ia, IIş-ţ,

IIIb,

PR

OB

AB

ILIT

Y

Improbable IIr, Vb-c IVc, Va IIIa,IVa-b, IIa,

Insignificant Minor Moderate Majour Catastrophic

EFECTS (GRAVITY)

The results of the qualitative risk analysis conducted for the operating phase shows

that most of the accident scenarios present a low or, very low risk, but the accidents in the

open pit such as accidental explosions and explosives handling/transport accidents, liquefied

petroleum gas tank explosion and cryogenic oxygen tank explosion, presents a moderate risk,

which involves the application of specific intervention procedures. Also, explosions inside the

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explosive magazine, dam breaking through and hydrocyanic acid emissions due to contact

between cyanide and hydrochloric acid in case of a major accident at the processing plant site

can have serious consequences, even if there is a very low production probability. As such it

is considered useful and necessary a more detailed analysis based on quantitative risk

assessment for these accident scenarios, which can be considered major potential accidents.

2. Detailed analysis of the relevant risk accidents

To assess the risk associated to major potential accidents identified by qualitative

analysis, is also used the methodology based on consequences’, also called "deterministic

approach" based on assessment of the consequences of possible accidents, without

quantifying the probability of production of these accidents, thus avoiding the inherent

uncertainties that occur in explicitly quantifying of the potential accidents occurrence

frequency.

This method has a rational basis similar to „imagine the worst scenario”. It is

considered that if for the worst accident imagined scenario, there are taken sufficient

measures to protect the population then, for each possible accident, less serious than the

worst, the measures to protect population will also be sufficient.

To identify the worst possible scenario, there are defined several "reference scenarios

(hypotheses), assessing the consequences arising from their production, there is identified the

‚worst scenario’ that is taken into account in order to analyse area location of risk generator

unit.

Consequences of accidents are taken into account quantitatively, by calculating the

distance where physical size that describes the consequences (e.g. Toxic concentration)

reaches a value (a threshold) limit corresponding to performance beginning of undesirable

effects.

In addition to distance proper lethal threshold value of the physical measure that

describes consequences, there is also estimated another distance, corresponding to the

beginning of "irreversible effects". This distance is used to separate areas with sensitive

population (schools, hospitals) or of densely populated areas of sources of danger.

Effects resulting from an accident depend on scenario type that defines the analyzed

accident and the value of specific determined indicator.

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2.1. Atmospheric hydrogen cyanide emissions associated risks

Gaseous hydrocyanic acid emission produced through sodium cyanide mixture with

hydrochloric acid

Previously presented qualitative analysis has shown that "the worst imagined

scenario’ for hydrocyanic acid (toxic dispersion) is the accident within there would have

taken place simultaneous cyanide solution discharge and that of hydrochloric acid and

mixture of these two seepages/leakages. Because simultaneous damage probability of cyanide

and hydrochloric acid storage vessels resulted in the mixture of the two solutions is extremely

low (due to long distances between hydrochloric acid storage site towards cyanide storage

site), was considered a ‚maximum possible scenario’ that consists in breaking of one

hydrochloric acid transportation tank when the 1000 l of hydrochloric acid drain and interfere

with an equimolecular sodium cyanide solution quantity. In this situation it can be considered

that the whole quantity of hydrocyanic acid formed suddenly passes into a gaseous form and

disperses into atmospheric air from damage area. The most unfavourable situation is the one

when initially discharges of hydrochloric acid, over which there takes place cyanide drainage,

when released hydrocyanic acid quantity is maximum. In this situation it produces acid

neutralization by sodium hydroxide and sodium cyanide until acid exhaustion after which

solution is diluted by cyanide excess. Maximum release of hydrocyanic acid takes place

during initial period when heat quantity released from neutralization exothermic reaction

strongly heats a relatively low liquid quantity.

Considering a hydrochloric acid solution concentration of 36 % and a density of 1.15

kg/l, maximum quantity of pure hydrochloric acid contained within drained solution is of 414

kg.

The 23 % sodium cyanide solution has a density of 1.25 kg/l, and also contains

variable quantities of sodium hydroxide (1-3%) and sodium carbonate (0.5 – 2.5 %). For

calculations we will consider that solution has a content of only 1% NaOH.

In these conditions, a perfect mixture of the two solutions initially assumes

hydrochloric acid neutralization with sodium hydroxide from cyanide solution based on

reaction

NaOH + HCl = NaCl + H2O

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When there are consumed approx. 5 % from hydrochloric acid and the rest reacts with

sodium cyanide forming hydrocyanic acid:

NaCN + HCl = HCN + NaCl

Hydrogen cyanide quantity formed in these conditions is of 290 kg consuming 528 kg

NaCN pure that is to say approx. 1.84 m3 solution 23 %.

For consequences analysis of such kind of an accident, there proceeded to the

simulation of release into the atmosphere of the 290 kg of hydrogen cyanide so formed,

considering that ‚solution pool’ accumulated on a surface or approx. 200 m2.

In order to assess the way in which hydrogen cyanide release into atmosphere takes

place, there proceeded to this release modelling using mathematical SLAB model that

simulates atmospheric release of gaseous emissions more dense than the air. This model

initial version was developed by Morgan, model further development being financed by

USAF Engineering and Services Centre (from 1968) and by American Petroleum Institute

(from 1987). SLAB model current version can treat different situations as for example:

instantaneous emissions, with a finite duration or continuous from different sources: liquid

pool that evaporates on ground level, horizontal jet or vertical jet positioned on different

heights above ground (discharge stack situation) or instantaneous emissions on ground level.

SLAB mathematical model is based on superficial layer theory. Concentration

variation description takes place through a differential equations based on total mass

conservation and on components, on energy and on impulse of the 3 directions. This

mathematical model is completed by equations that describe the formation of gas plume as

well as, by equations for gas physical characteristics modelling. Gas release simulation

through SLAB model takes place through mathematical equations integration model on wind

direction.

SLAB model solving allows only average concentration on wind direction.

Concentration distribution calculation on perpendicular directions y and z (width, respectively

height until gas) takes place through one distribution model distribution considering.

SLAB View programme is Windows interface for SLAB model of gas more dense

than air release simulation and was accomplished by Canadian company Lakes

Environmental Software.

In order that hydrochloric acid exposure have effects on human health, one person has

to stay within the area where discharge took place, within one toxic cloud, without any

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respirators for a certain period of time, the effects being more serious as this exposure period

of time is longer.

Threshold values * used for effect on population are the followings:

LC50 – (Lethal concentration with 50% death of victims) is a value of toxic substance

concentration value into atmospheric air expressed in ppm or mg/mc, calculated or

experimentally determined for certain exposure duration (usually 30 min), beyond which

effects are considered lethal. For hydrocyanic acid LC50 is 100 ppm. Within the area limited

by this concentration threshold is defined as High mortality area (Area I).

IDLH (Immediately Dangerous to Life or Health Air Concentration Values –

Immediate danger for life and health) is atmospheric concentration of any toxic substance,

corrosive or asphyxiated that present immediate threat for life or that can cause irrevocable

unfavourable effects on health or interfere into individual capacity to escape from a dangerous

atmosphere. Is expressed in ppm or mg/mc and is determined for an exposure period of time

of 30 min. For hydrocyanic acid IDLH is 50 ppm. In the delimited area IDLH value is defined

as Area health damages (Area II).

Note: *Threshold values define areas where life (area I) respectively population

health (area II) can be exposed to danger.

Initially there proceeded to an analysis regarding the effects that different parameters

have of release results, in view of choosing the conditions in which effects are maximum. In

this respect there were carried out a simulations series, for different possible situations,

conclusions being the following:

- temperature variation of the solution from which hydrogen cyanide release takes

place (within an interval between -20 0C and + 50

0C) does not have a significant effect on

dispersion results, as such we have adopted a 25 0C temperature (boiling hydrogen cyanide

temperature) for all simulations carried out;

- form of the liquid from which hydrogen cyanide emission takes place (in what

regards layer surface and thickness) does not have effects on release;

- land surface characteristics above which release takes place, significantly influences

release, as such on simulation there were considered land characteristics as being relatively

free lands, with rare buildings and low;

- measuring height (from ground level) of hydrogen cyanide concentration does not

have significant effects on release (within area considered as ‚breathable atmosphere’ on the

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interval from 0 to 4 m), as such results representation is carried out for concentrations

calculated on 2 m height above ground.

- wind speed significantly influences toxic cloud characteristics, in the sense that a

high speed generates an elongated cloud, that quickly spreads on a relatively long distance,

with a relative rapid reduction of concentrations and a low speed generates a larger cloud, that

slowly spreads on a large distance, with a slow reduction of concentrations. The areas affected

by concentrations and longer exposure time are larger in case of wind low speeds and as such

this situation is more dangerous. In the presented simulations there is used a speed of 0.5 m/s

(much lower than the specific multi-annual average of the area);

- atmospheric stability is another factor that has a major influence on release,

atmospheric stability state being the unfavourable one and as such used on presented

simulations;

- air relative humidity does not significantly influence release and as such we have

used the value of 80 %;

- atmospheric temperature is one of the parameters that does not significantly

influence release, even though a high temperature is favourable to release. As such we used

on presented simulations a temperature of 20 0C.

Toxic cloud is formed above ‚liquid pool’ (on ground level) through hydrogen cyanide

evaporation resulted from cyanide solution mixed with hydrochloric acid and then displaces

on wind direction.

Current/ at moment hydrogen cyanide concentration evolution calculated through

simulation depending on source distance is presented in Figure 4.4:

Figure 4.4 . Hydrocyanic acid momentary concentration evolution

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In Figure 4.5 there are presented the areas affected by the concentrations above LC50

respectively IDLH (exposure duration of 30 minutes) and that represent safety areas that must

be considered in case of such an accident:

Figure 4.5. Safety areas that must be considered in case of one hydrogen cyanide

emission

We note that:

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- high mortality area spreads until 170 m from the source

- area with damages on health spreads until about 365 m

which means that in such an accident occurrence, most of the persons caught unprotected by

the toxic cloud will suffer significant effects.

Analyzing these results in the context of site location within the area of a toxic source,

we note that there will be affected by toxic concentrations only land surfaces from industrial

perimeter (plant enclosure) and part of the adjacent land.

Volatilization is a source of loosing cyanide in CIL process, but through maintenance

of a sufficiently high pH (above 10.5) emissions into the atmosphere are minimum and do not

reach dangerous concentrations within working area. An accident scenario where a

hydrocyanic acid significant emission can produce into the atmosphere is the one where takes

place a pH significant decrease into CIL plant leaching tanks due to some pH control systems

failure. For assessment of risks associated to such an accident there proceeded to hydrogen

cyanide quantity calculation possible to be released from the surface of the 6 CIL tanks

considering that cyanide suspension has a maximum concentration of free cyanide (300 mg/l)

and pH decreases under 9.2 when practically the whole formed hydrogen quantity is

volatilises and is released into the atmosphere (emission is maximum).

Emission rate calculation was carried out using recommendations “Emission

Estimation Technique Manual for Gold Ore Processing”, 1999, National Pollutant Inventory

(NPI), Australia:

Calculation formula:

E = ({0.013 * [HCN(aq)] + 0.46} * A * T / 106) * 1000

where:

E = HCN emission (kg)

[HCN(aq)] = [NaCN] * 10(9.2 - pH)

[NaCN] = NaCN concentration within CIL tanks (mg/l)

pH = pH within CIL tanks

A = Total surface area (m2) of CIL tanks (m

2)

T = Emission period (hours)

Input data :

Emission surface = 6 x 78.5 = 471 m2

Tank diameter = 5 m

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Tank surface = 78.5 m2

Average concentration of free cyanide within tanks:

300 mg/l CN = 565.4 mg/l NaCN

pH = 9.2

T = 1 hour

Calculated emission rate is of 2.053 kg/h HCN.

Although the deviation from normal operation pH cannot last very long (besides

automatic control system there are periodically sampled lab probes also) we will consider that

this emission can last maximum 10 hours.

Hydrogen cyanide simulation release into the atmosphere was carried out similarly

with the previous case, the only difference being the height on which, release takes place (12

m – above tanks). The evolution of momentary concentration of hydrocyanic acid calculated

through simulation of function of distance from the source is presented in the figure 4.6:

Figure 4.6 - Hydrocyanic acid momentary concentration evolution (12 m – above

tanks)

Simulations results show that in this case there are not reached toxic concentrations

into the atmospheric air on respiration level above LC50 respectively IDLH for exposure

durations of 30 minutes even if maximum momentary concentrations within toxic cloud

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above the level of 100 ppm respectively 50 ppm. These are registered until distances of 90 m,

respectively 160 m.

Thus in such an accident case there is necessary only an attention area establishment

within plant enclosure.

2.2. Liquefied petroleum gas tank associated risks

Accidents consequences taken into consideration quantitatively, through distance

calculation where physical measure that describes consequences (thermal radiation, power,

overpressure on shockwave front) reaches a value (threshold) limit corresponding to

beginning of unwanted effects performance. It has to be mentioned that within national

legislation there are not adopted yet such values, thresholds used in the present work are

according to some other country from EU legislation (values are not unitary on EU level).

Effects generated by one accident occurrence depend on the type of scenario that

defines the analysed accident and special determined indicator value.

Damages cause depending on thermal radiation intensity are summarized in table 4.7.

Table 4.7 Damages occurred depending on thermal radiation function

Thermal radiation intensity

(kW/m2)

Damage type

37.5

Process equipment destruction 100 % deaths after 1 min exposure long, 1% deaths after a 10 seconds exposure

25.0

Minimum energy for wood lighting on a long exposure

without flame. 100 % deaths on a minimum 1 min.

exposure, serious injuries (wounds) after a 10 seconds

exposure

12.5

Minimum energy for wood lightning on exposure with

flame. 1 % deaths on a 1 min. long exposure, first degree

burnings for a 10 seconds exposure

4.5

Pains caused if exposure is longer than 20 sec but ulcers

(curl) are less probable.

1.6

Causes short term discomfort for long term exposures

Threshold* values used for the effect on population are the following:

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For thermal radiations value on fire:

- 12.5 kW/m2 for high mortality area (area I);

- 5 kW/m2 for irreversible injuries area (area II).

For energy value on BLEVE** explosives:

- Fire ball radius for high mortality area

- 200 kJ/m2 for irreversible injuries area

According to French methodology, the two threshold are:

- 1800[(kW/m2)4/3]·s , for high mortality area

– 600 [(kW/m2)

4/3]·s , for irreversible effects area

For released gas concentration value on fires type flash fire:

- LEL*** (area I)

- 0,5 LEL (area II)

Note: *Threshold values define areas in which life (area I) respectively population

health (area II) can be jeopardized.

** In some EU countries there are used for BLEVE explosions the same threshold

values as for thermal radiation on fire. Presented values are according to Italian legislation

where threshold values for BLEVE are power unities. Threshold values use for radiant

energy, where it takes into consideration fire ball duration, has as a result radius for relevant

areas sensible reduced than if threshold for thermal power were used (radiant heat).

However it is considered that this approach is more realistic because thermal

radiation effects depend on exposure duration, that in case of BLEVE explosions were very

short (from a few seconds to about 30 sec), the way it will also result from carried out

simulations.

*** LEL „Lower Explosive Limits” – explosion inferior limit

Tank rupture

BLEVE type explosions can be produced through two mechanisms:

- through tank breakage as a consequence of corrosion and to some very big

mechanical stress: ‚Cold BLEVE’;

- in case of involvement into a fire of installation parts (tanks, fuel tank, motor tank

trucks, pumps, pipeline portions) that contain liquefied petroleum gas and that are closed:

‚warm BLEVE’, when due to warming up there will occur material weakness and enclosure

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over pressurization, followed by construction material breaking.

Explosive blast effects calculation and of tank fragmentation in case of

explosion can be divided into two stages. On the first stage there is calculated the available

power, and on the second stage effects are calculated, taking into consideration power

calculated on the first stage:

Eav = eav · Mfl (J) (1)

where: Eav – total released power (J)

eav – specifically work carried out by expansion liquid (J/kg)

Mfl – released phase mass (kg)

There are no precise methods for calculation of the number of fragments

thrown into the air after a BLEVE explosion. In literature can be found estimations based on

accidents investigations. In case of tanks local resistance reduction, number of the fragments

is estimated to 2 pieces, but in case of over pressurization the number of fragments depends

on tank shape: for cylinders 2 or 3 pieces, for spheres between 10 and 20 pieces. In case of

many fragments, their mass - Mv in (kg), is calculated using average mass. Fragments speed,

vi, can be calculated with Baum empirical formula [10]:

v

avke

iM

EAv

⋅⋅

=

2 (m/s) (2).

Released power fraction, Ake (-), that transforms into kinetic energy, in case of BLEVE

phenomenon is estimated to 4 % from total energy [10].

EFFECTS programme was used in order to calculate these indicators, Environmental

and Industrial Safety that is developed for industrial accidents effects and consequence

analysis. Program was developed by TNO Built Environment and Geosciences Company –

Netherlands and programme models are based on „Yellow Book”, internationally recognised

as a standard in risk analysis issuance.

For some potential accidents simulation there were used the following models:

- for explosions on liquid petroleum gas tanks, there was used ‚BLEVE’ model with

„ball fire” formation.

- for fires, taking into considerations emplacement specific and one possible accident

predictable evolution, there was used scenario model „JET FIRE” (fire type „fire jet”) for

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arson of some liquefied petroleum gas under pressure and „FLASH FIRE” for ignition of

some gas leakage.

Simulation was carried out with propane.

For simulations there were imagined reference scenarios presented below that were

considered significant for situation from the emplacement.

Scenario 1. BLEVE type explosion of liquefied petroleum gas of 10 tons

After involvement into a fire of a liquefied petroleum gas tank, as a consequence of

fire exposure, there produces a pressure increase inside the tank and construction material

weakness, that produces BLEVE explosion of tank.

Below there are presented the results obtained through simulation with EFFECTS

programme.

Inputs

Chemical name Propane (YAWS)

Total mass in vessel (kg) 10000

Initial temperature in equipment (°C) 51,2

Burst pressure of the vessel (bar) 17,6

Max. distance in graphs (m) 1500

Take protective effects of clothing into account No

Outputs

Duration of the Fire Ball (s) 9

Max Diameter of the Fire Ball (m) 124,96

Max Height of the Fire Ball (m) 187,44

Max View factor of the Fire Ball (%) 28,076

Max Atmospheric Transmittance (%) 73,253

Max Surface Emissive Power of the Fire Ball (kW/m2) 400

Max Heat Radiation (kW/m2) 73,374

Heat Radiation Dose (s*(kW/m2)^4/3) 1059,8

Percentage Fatality 1st Degree Burns (%) 100

Percentage Fatality 2nd Degree Burns (%) 75,468

Percentage Fatality 3rd Degree Burns (%) 51,233

First high mortality area is given by fire ball radius, that is of 62.4m. In figure 4.8

there is represented fire ball diameter depending on time.

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Figure 4.8. Fire Ball diameter depending on time

Diameter of the Fire Ball vs. Time

Session 1

Time [s]9,08,07,06,05,04,03,02,01,00,0

Dia

me

ter

of th

e F

ire

Ba

ll [m

]

130

120

110

100

90

80

70

60

50

40

30

20

10

0

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According to French methodology, that takes into account the exposure time (it

calculates thermal load depending on distance), the following distances are obtained:

THRESHOLD 1 – corresponding to high mortality area, 1800[(kW/m2)

4/3]·s = 73.2 m

Note: This threshold is practically equivalent to fire ball radius.

THRESHOLD 2 – area with irreversible effects, 600 [(kW/m2)

4/3]·s = 133.2 m

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Figure 4.9. Thermal load depending on distance

Heat load vs. distance

Session 1

Distance [m]300250200150100500

He

at

loa

d [

s*(

kW

/m2

)^4

/3]

6.500

6.000

5.500

5.000

4.500

4.000

3.500

3.000

2.500

2.000

1.500

1.000

500

0

In figure 4.10 there are represented on map the affected areas and on chart from

figure 4.11 there is presented burnings evolution depending on distance.

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Figure 4.10 . Map of affected areas in case of liquefied petroleum gas tank explosion

Figure 4.11 Burnings evolution on persons exposed depending on distance from the source

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Session 1 - First Degree Burns Session 1 - Second Degree BurnsSession 1 - Third Degree (Lethal) Burns

Distance [m]200100

Bu

rns [

%]

90

80

70

60

50

40

30

20

10

0

From map representation there can be observed that area 1 includes elution

installation, steam chamber, sewage treatment plant and a part of Detox 1 installation. Besides

objectives mentioned on area 1, area 2 includes also Detox 1 neutralization installation

integrally, CIL installation and a part of Albion installation.

Effects can still be considered as being of low gravity because in these areas persons

work most of the time within buildings, thus being protected of thermal radius generated of

such an accident.

Scenario 2. Fire produced through ignition of a liquefied petroleum gas discharge from

duct (jet fire)

There is considered production of a leakage through a broken pipe, followed by

ignition of under pressure drainage and production of a fire type „Jet fire”, flame length and

diameter depending on drainage pressure and on its dimension.

In order to be able to carry out fire simulation there was first carried out a liquefied

petroleum gas drainage simulation on a pipe of Dn 80mm, considering tank pressure equal to

liquefied petroleum gas vapours pressure on 20 0C . The obtained results present as follows:

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Inputs Chemical name Propane (YAWS)Use which representative step First 20% average (flammable)Type of release Release from vessel through (a hole in) pipePipeline length (m) 1Pipeline diameter (mm) 80Hole diameter (mm) 80Hole rounding Rounded edgesDischarge coefficient (-) 1Height difference between pipe entrance and exit (m) 0Height leak above tank bottom (m) 0Initial temperature in vessel (°C) 20Vessel volume (m3) 25Vessel type Horizontal cylinderLength cylinder (m) 7,6Filling degree (%) 80Pressure inside vessel determination Use vapour pressureInitial (absolute) pressure in vessel (bar) 8,3568Type of calculation Calculate until device is emptyTime t after start release (s)

Results Initial mass in vessel (kg) 10109Initial (vapour) pressure in vessel (bar) 8,3568Time needed to empty vessel (s) 352,2Massflowrate at end outflow (kg/s) 0Total mass released (kg) 10051Pressure in vessel at end outflow (bar) 1,0151Temperature in vessel at end outflow (°C) -43,601VapourMass fraction at end outflow (%) 100Liquid mass in vessel at end outflow (kg) 0Vapour mass in vessel at end outflow (kg) 58,633Height of liquid at end outflow (m) 0Fillingdegree at end outflow (%) 0Exit pressure at end outflow (bar) 1,0151Exit temperature at end outflow (°C) -43,601Maximum mass flow rate (kg/s) 37,01Representative release rate (kg/s) 36,689Representative outflow duration (s) 274Representative temperature (°C) 8,8639Representative pressure at exit (bar) 6,1572Representative vapour mass fraction (%) 3,2795

After simulation there resulted a maximum flow rate of 37,01 kg/sec with which there

was still continued fire simulation, the results of which present as follows:

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Inputs Chemical name Propane (YAWS)Mass flow rate of the source (kg/s) 37,01Distance from release (Xd) (m) 100Take protective effects of clothing into account NoPredefined wind direction NOutflow angle in XZ plane (0°=horizontal; 90°=vertical) (deg) 0

Outputs Length of the flame (m) 62,718Width of the flame (m) 7,8398Heat radiation at Xd=100m (kW/m2) 4,1179Fraction of mortality at X (%) 0

After fire simulation there result the following:

- there is no area with a high mortality, only flame itself, with a length of 62.71 m can

produce important injuries to directly exposed persons;

- irreversible injuries area length (thermal radius higher than 12,5kW/m2): 70.75m.

In the following figures there is presented radiant heat evolution depending on

distance from the source and respectively gravity of burnings produced to persons exposed

depending on distance from the source.

Figure 4.12 Radiant heat evolution depending on distance

Heat radiation vs. distance

Session 4

Distance [m]1009080706050403020100

He

at

rad

iatio

n [

kW

/m2

]

20

19

18

17

16

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Figure 4.13 Gravity of burnings produced depending on distance from the source

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Session 4 - Lethal burns Session 4 - Second degree burnsSession 4 - First degree burns

Distance [m]1009080706050403020100

Bu

rns [

%]

100

90

80

70

60

50

40

30

20

10

0

2.3. Risks related to cryogenic oxygen tank explosion

The imagined scenario is the one that, after a damage on tank exterior encasing, there

produces sudden vacuum loss (thus also thermal isolation loss of cryogenic tank) followed by

a temperature increase inside tank simultaneously with sudden increase of pressure from

within the tank, cracking and its BLEVE explosion.

For oxygen tank explosion there was used BLEVE model with tank breakage of

EFFECTS programmes and the results obtained present as following:

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Inputs Chemical name Oxygen (YAWS)Cause of vessel rupture Pressure liquefied gas, BLEVEVessel type CylinderLength/diameter ratio of the vessel 5Burst pressure vessel (bar) 37Vessel volume (m3) 57Filling degree (%) 95Liberated Energy (kJ) 1,1902E06Ambient temperature (°C) 20Fraction of liberated energy going to kinetic energy (%)

4

Fragment distribution 2 caps and bodyMass of empty vessel (kg) 3000Mass of heaviest piece (body when cylinder ruptured in 3) (kg)

2000

Threshold overpressure (mbar) 70

Outputs Peak overpressure at Xd (mbar) 14,245Pressure impulse at Xd (Pa*s) 28,274Mass of heaviest fragment (F1) (kg) 2000Initial speed of F1 (m/s) 60,749Maximum range of F1 (m) 279,41Mass of lightest fragments (F2) (kg) 500Initial speed of F2 (m/s) 60,749Maximum range of F2 (m) 308,51Damage (general description) at Xd No damage or very minor damage

Damage to brick houses at Xd Damage to roofs, ceilings, minor crack formation in plastering, more

than 1% damage to glass panels (1 - 1.5 kPa)Damage to typical American-style houses at Xd

No damage or very minor damage

Damage to structures (empirical) at Xd No damage or very minor damage

The obtained results show that the area with a high mortality (Area I with overpressure

over 300 m bars) is within a circle with a radius of 59 m and the area with irreversible injuries

(Area II with overpressure over 70 m bars) is within a circle with a radius of 128 m.

In figure 4.14 there is represented overpressure evolution depending on distance and in

figure 4.15 the map with risk areas representation, associated to this scenario.

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Figure 4.14 . Overpressure depending on distance

Overpressure vs Distance

Session 17

Distance from centre of vessel [m]1009080706050403020100

Ove

rpre

ssu

re [

mb

ar]

35.000

32.500

30.000

27.500

25.000

22.500

20.000

17.500

15.000

12.500

10.000

7.500

5.000

2.500

0

Figure 4.15. Map of affected areas

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There can be observed that within area 1 there is only oxygen plant and area 2 also

includes Albion installation and a good part of the maintenance workshop.

Taking into consideration that most of persons that may be present within those areas

work within some buildings, effects can be considered less serious, only persons from the

next proximity of the tank involved into the accident will have to suffer more serious injuries.

2. 4. Risks associated to explosive materials

a. AMFO mixture explosion within open pit

Explosions seismic risk is characterized through material particle oscillation speed.

Oscillation speed depends on many factors: physical-mechanical characteristics of formations

crossed by seismic wave, their sequence and extension, rocks structural faults (size, sequence

and their orientation), distance covered by seismic wave (distance between explosion focus

and the measuring point) shooting works technology and load distribution and explosion load

measure.

This speed is determined through field measurements or using the relations provided

by the specialized literature. The formula used for oscillation speed calculation is:

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V = k(Q/R3)

1/2 where:

- k- coefficient that depends on material characteristics (ground) from the area;

- Q – explosive quantity involved into explosion (kg equiv. TNT);

- R – distance to the place of explosion

From experience of some shooting works carried out in relatively similar conditions

(when there were carried out measurements of oscillation speed) there was determined an

average value for coefficient k = 30 that will be adopted also for the following calculations, so

formula for oscillation speed calculation in case of shooting at Certej mining perimeter will

be:

V(cm/s) = 30(Q/R3)1/2

For explosives assessment effects on area objectives there were adopted DIN 4150/83

German normative provisions presented in table 4.16:

Table 4.16 . DIN 4150/83 - German normative provisions for explosions assessment

effect on area objectives

Speed (mm/s) Type of building

< 10 Hz 10-50 Hz 50-100 Hz

Headquarters and plants

buildings

20 20-40 40-50

Residence buildings 5 5-15 15-20

Historical monuments 3 3-8 8-10

There can be observed that the smallest value is of 3 mm/s, and that we will consider

maximum admitted speed for the worst case for possible accidents produced on explosive

transport route. For accidents within the open pit site we will consider maximum admitted

speed for buildings within plants, respectively 20 mm/s.

Overpressure on shockwave front is as well as a parameter that allows assessment of

explosion effects on constructions and on people.

According to safety distances calculation methodology from “Technical rules

regarding possession, preparation, experimentation, destruction, transport, storage, handling

and use of explosive materials used in any other specific operation in activity holders, as well

as art-firers and pyrotechnic authorisation’ approved through government decision 536 from

the 4th of July 2002 ANNEX No.3 a), minimum safety distances towards surrounding exterior

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objectives will be established after over-pressure value from shockwave front, calculated after

relation:

∆pf = 0,84 λ+ 2,7 λ 2 + 7 λ 3,

Where :

∆pf = shockwave front overpressure (kg/cm2);

λ = q 1/3

/R,

where:

q = explosive materials expressed in Trotyl equivalent, the destructive effect of

which extends on the longest distance (kg);

R = distance measured from the focus until de considered objective (m).

Damages caused in case of some explosions depend on overpressure from shockwave

front are summarized in the table below, extracted from Annex no.3b to Government Decision

HG 536/2002 modified through Government Decision 1207/2005 (Explosive materials rule)

(Table .4.17):

Table .4.17 Extracted from Annex no. 3b to Government Decision 536-2002

Crt. Exterior objective type Overpressure value on shockwave front

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No.

Total loss Import

ant

loss

Average loss Easy loss Insignificant

loss

1 Reinforced concrete buildings

2 Brick buildings with several floors

3 Brick buildings with a few floors

4 Wooden houses

5 Industrial buildings with metalic

frame

6 Networks of local household

7 Railway metalic bridges

8 Railway

9 Railway gaskets

10 High pressure air lines

11 Air transmission lines on

wooden pillars

12 Underground cables

13 Feeders and transformer plants

14 Retaining walls

15 Dams and dykes

16 Completely broken windows

17 Partially broken windows

18 Human injury

a)certain death

b) very severe injuries, virtually

incompatible with life

c) severe injuries (fractures,

internal bleedings)

d) average injuries (contusions,

deafness)

e) easy injuries (contusions,

ringing ears)

* Depending on depth where they were installed

a. Explosion of some un-detonated cargo

This scenario was taken into account because AMFO explosive mixture is prepared

from ammonium nitrate and gas directly on place of use (thus AMFO can be involved in a

possible accident only within open pit site) but explosion itself that carries out the process of

rocks removal cannot be considered an accident.

For accidental explosions effect calculation on a unit shooting, there was taken into

account the hypothesis of involving into the accident of an explosive quantity equivalent to

the one used for a baring unit (that is also covering the mining blocks). Explosive maximum

quantity in TNT equivalent involved into the explosion will be of:

980 kg Nitramon * 0.733 kg TNT/ kg Nitramon + 4 kg dynamite * 1.3 kg TNT/kg

dynamite = 724 kg TNT equivalent.

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There were calculated oscillation speeds on different distances from explosion focus in

case of a load of 724 kg equiv. TNT instantly detonated.

The obtained results are presented in table 4.18.:

Table no. 4.18 Oscillation speeds on different distances from explosion focus in case

of a load of 724 kg equiv. TNT instantly detonated

Crt. No. Distance to explosion focus

[m]

Oscillation speed

[mm/s]

1 25 65

2 50 23

3 55 20

4 75 12.4

5 100 8

6 125 5.8

7 150 4.4

Results in case of instantaneous explosion (accidental) of a load of 724 kg TNT

equivalent oscillation speed maximum admitted value will be exceeded only on distances

smaller than 55 m to explosion focus. Because such an accident can produce only within open

pit site, the effects can be considered significant only for the personnel and equipments

situated in the next proximity of focus.

Overpressure in shockwave front effects calculated using the previously presented

relations, on industrial buildings and on personnel, in case of an accidental explosion of 724

kg TNT equiv. These are presented in the table below.

Overpressure effects on shockwave front calculated using the previously presented

relations, on industrial buildings and on personnel, in case of an accidental explosion of 724

kg TNT equivalent are presented in table 4.19.:

Table no. 4.19 Overpressure effects on shockwave front in case of an accidental

explosion of 724 kg TNT equivalent

Crt.

No.

Overpressure

kg/cm2

Distance to

explosion focus

m

Effects on industrial

buildings with a

metallic frame

Effects on personnel

1 1 24.81 Total destruction Serious trauma virtually


2 0.8 27.77 Total destruction Serious trauma virtually


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3 0.5 35.75 Serious damages

Serious trauma

(fractures, internal

bleedings)

4 0.3 48.3 Average damages Average trauma (contusions, deafness)

5 0.2 62.81 Easy damages Easy trauma (easy

contusions, ringing ears )

6 0.1 103.79

Insignificant damages

(windows complete

breaking)

Insignificant trauma

It results that shockwave overpressure in case of accidental explosion of a load of 724

kg TNT equivalent are insignificant on distances over 104 m, on buildings as well as on

personnel.

b. Ammonium nitrate explosion ( - NA)

In normal storage, handling and use conditions, NA is stable.

However NA is an oxidizing agent that through heating at high temperatures indoors

(ex: pipelines, etc.) will achieve at a high pressure, and these lead to violent reactions or

explosions, especially if they are contaminated with dangerous substances (combustible

materials and lubricants, reducing agents, acids, sulphides, dyes, chlorides, chromate, nitrates,

permanganate, metallic powders).

Manure has a high detonating resistance, but this resistance decreases in presence of

contaminants or at high temperatures.

NA can maintain combustion. NA has a very complex behaviour and that is why it has

been studied especially. There are three main hazards associated with NA:

- The decay instability;

- Fire (due to its oxidizing nature);

- Explosion;

The most important parameters that influence hazards presence are: particles size,

particles density, porosity, nitrogen content, ambient temperature.

NA itself does not burn and is not combustible. As am oxidizing substance it can

maintain burning and can intensify a fire even in lack of air, but only as much as combustible

or inflammable material is present. During burning process it decomposes into nitrogen

oxides and ammonia, both toxic. Indeed, toxic effects of the produced gas, from which the

most toxic is nitrogen dioxide, represents the dominant risk because the risk of an explosion

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occurrence is considered as being too low. In addition melting temperature of NA pure is that

of 169.6 oC. During melting process there are absorbed a part of the received energies and

often the melted product drains and energies are released outdoors.

NA hot solution, as solid nitrate can be fire dangerous. NA hot solution can initiate

textile or wooden material ignition. NA impregnated clothes left on a hot surface can ignite in

time.

Fires where NA is involved cannot be extinguished through chocking off, because NA

can produce the necessary oxygen to burning maintenance. Water is the most suitable for NA

involved fire extinction, the most efficient method being the effective water flooding of the

area covered by fire.

NA can produce explosion through one of the following three ways:

• Heating indoors;

• accelerated decomposition reactions – self-heating through thermal decomposition;

• detonation – initiation by shock by another explosive or mechanical impact.

Heating indoors becomes a risk in case of inadequate ventilation.

NA rapid decomposition leads to a pressure considerable increase that eventually may

cause explosion. As well melted NA is much more sensitive to initiation than solid material.

A decomposition accelerated reaction is reached when heat generated by reaction exceeds the

heat lost within extremely dangerous limits. For pure NA these conditions are extremely hard

to accomplish due to low decomposition rate and to endothermic effect when this one is not

restricted.

Uncontaminated NA is very difficult to detonate. Neither flame, nor spark, nor

frictions cannot trigger a detonation. Initiation thorough shockwave needs a huge energy

quantity. Sensitivity to shock initiation increases with temperature, presence of combustibles,

reagents substances and voids and bubbles within NA substance with a low density being

porous is significantly more sensitive than high density fertilizer. The impact produced by

falling objects does not release sufficient energy for an explosion initiation.

Another very important factor is the minimum dimension or the NA load diameter. As

nitrate heap size increases, the risk for explosion also increases.

The critical diameter of load in the minimum diameter required to achieve an

explosion. NA with a high density has a very large critical diameter of load, determining that

explosion within entire mass be very difficult > 7m on a load density of 1.0 g/cm3.

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There is a certain confusion and uncertainty in literature and in security reports

regarding fertilizer explosion power. This one can be followed until the question – can it be

possible that a fertilizer stack be detonated or only deflagrated? Experiments have shown that,

there cannot be possible neither of the above, only if at least a part of the respective stack is

heated up over its melting point. Detonation, that is characterized through a supersonic

pressure wave that displace through material, can occur only is explosive dimensions are

larger than a particular value known as a critical load diameter. For solid fertilizer, this

diameter is about 3 m which implies the fact that a quantity smaller than 300 t is less probable

that it will detonate. Diameter that corresponds to melted NA is of only 10 cm.

NA with a low density is relatively much sensitive to detonation. It has a critical

diameter of load much smaller and as a consequence a smaller initiation load is sufficient for

detonation. NA content affects the explosive potential. Researches have shown that explosion

risk is reduced if NA content is limited to, for example, 90% (31.5% N) with another

reduction is this limit is decreased to 80% (28% N). Anyway, there must be recognized the

fact that explosion potential risk – also somewhat reduced – still remains.

Deflagration is not constrained by dimensions and is considered when pressure wave

generated by a subsonic combustion travels through material. In certain conditions, released

energy and damages produces by the two processes (detonation and deflagration) in a NA

probe can be different, but within a hazard analysis, it is not used to make the distinction

between these ones and to refer only to explosion.

Deflagration and transition phenomenon can be developed in conditions of a large fire

or a violent massive decomposition, through creating the necessary conditions. Anyway, both

of them – clean substance or contaminated (or with combustibles) with NA needs existence of

a very high pressure for this phenomenon occurrence. There is less probable that these

conditions are met in normal storage conditions. Last but not least, is important to be

mentioned the fact that in the so-called normal storage conditions, NA decomposition can

occur.

General opinion regarding hazards that imply NA is that, in case of an extinguished

fire on a fertilizer storage yard, a pool of liquid NA will be formed at the end of fire closest

stack. If this pool is hit by a high speed projectile (e.g. A falling object or a part of an

exploded drum) then there takes place a local explosion that will transmit a shockwave within

fertilizer main stack that didn’t melt. If this stack contains less than 300 t, it will not support a

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detonation, but will deflagrate and, by doing this, will release an energy quantity equivalent to

41 t of TNT. This number is calculated on base of an equivalence of NA TNT with an

explosion power of 55% and an efficiency of 25%. Overpressure hazard field of 6.9·103 Pa (=

1 psi = 0.069 bar) for such an explosion is of 600 m.

It is supposed that NA outdoors stacks are not capable to explode because the

probability that explosion entails one beam collapse into a melted pool is very reduced.

TNT model application for explosive power calculation

Because an explosion is a rapid conversion of a solid within a gas on a high

temperature, the essential parameters that govern explosive field represent gas quantity

produced and heat released through reaction, that determine maximum reached temperature.

Gas quantity usually produced expressed as a volume (V0) on 0 oC and a pressure of 1 atm on

1 kg of explosive. V0 is calculated from chemical reaction that represent explosive reaction,

treating gas as ideal gases.

Explosion heat represents heat quantity released during decomposition. Is determined

through chemical equation that represent explosion reaction where explosive products from

the right side are in a physical state corresponding to some pressure and high temperature

conditions of the explosion. Formed water is in a state of vapours.

2NH4NO3�2 N2 +4H2O + O2 + 118 kJ/mol

One explosion heat, measured on an explosive mass unity is designed by Qv and is

approximated through reaction heat. Although, there is no unique modality of determining Qv

and different thermo-dynamical relationships produce different results.

In conclusion, there is pointless to strive for a good accuracy within explosive field

because not only that final thermo-dynamical state of products is uncertain, but also physical

state of the sealing and storage conditions can have a significant effect on the released energy.

Calculations and experiments have determined explosion energy of the most regular

explosives, but in practice not all the energy that can theoretically be released is converted

into a shockwave. There are many reasons for this, but the main reason is that only an

explosive mass fraction really explodes – the rest releases. The report between real released

energy and the one theoretically available is usually considered as explosion efficiency.

Energy release by an explosion is therefore the product between explosive mass – M

(kg), explosion energy – Es (J) on 1 kg of substance and explosion efficiency. Explosion

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specifically energy is usually measured in terms of energy detonation of TNT and is

considered as explosive power:

Explosive power = Es / ETNT

where: Es – One kilo of substance decomposition (J)

ETNT – Detonation energy of one kg of TNT (J).

Because explosions consequences are documented in terms ofr TNT mass,

other substances explosions consequences are most conveniently determined through one

TNT mass calculation. This one is defined as:

TNT equivalent= M x (Explosive power) x (efficiency).

One substance TNT equivalent was established (EQTNT), effect of one explosion of M

kg from that substance is easily determined through reference to one explosion studied effects

of an equivalent TNT quantity.

A general problem regarding TNT model applicability for a material as NA is that lack

of information (scientific) regarding values that have to be used for explosion power and

efficiency. A second problem is represented by non-ideal behaviour of NA regarding

detonating properties. As a result, large scale explosions will probably show effects (on scale)

different than those from field test son the smallest scale. In Table E 4.20 is presented a

glance on some values offered by UK Health and Safety Executive (HSE UK). Table also

indicates high density fertilizer values (FGAN) and density reduced technical degree (TGAN)

as it is used in different UK companies.

Table 4.20 Power, efficiency and NA explosion equivalent

Substance

denomination

Explosive

power

Efficiency TNT

equivalent

Bibliographic

source

Ammonium nitrate 55 % 25 % 14

%

HSE, UK

FGAN 30 % 10 % 3

%

Miscellaneous

TGAN 40 % 25 % 10

%

Miscellaneous

Basis

Basically, TNT equivalent of a material can be determined from theoretical

considerations, from ‚small’ scale tests and from incidents. TNT equivalent which has

resulted as a consequence of damages observed during Toulouse accident is approximately

7.5-20%. In this field, the interpretation that has to be taken into consideration is the fact that

there always refers to a specific type of material. Finally, but not insignificant is the fact that,

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because NA is a non-ideal explosive, shock characteristics (peak pressure, duration, etc.) is

different from a shock from a TNT explosion. This also affects equivalence number.

TNT equivalent power in case of an explosive event is governed by material explosive

power (TNT equivalence) as well as, by process efficiency. TNT equivalent and NA

explosive efficiency varies from a bibliographic source to another.

For example, in case of NA, whether one explosion efficiency would be of 100%, then

TNT equivalence would be of 0.55. Nevertheless, efficiency is variable and depends on

factors that include retention quantity and initiation mode dimension.

For NA stored into large stacks, some industrial experts presently accept that 0.32 is

the factor that has to be multiplied with a TNT quantity. For example, assuming that there are

stored 100 t of pure NA, TNT equivalent weight would be of 32 t. In case of explosion of

32000 kg of TNT there would be necessary a protection distance from the buildings outside

the site of approximately 705 meters. It may be that this distance is substantially reduced

through NA storage in such a way as not to allow a mass explosion of total storage ca.

For simulation performance, there were considered the following three scenarios:

i. Explosion of a 30 t quantity ammonium nitrate situated within storage yard

ii. Explosion of one quantity of 10 t ammonium nitrate during transport towards the

open pit

iii. Explosion of a quantity of 8 t of ammonium nitrate during transport towards the

open pit.

To continue, there are presented the results of the simulations effects carried out by

using EFFECTS programme, Environmental and Industrial Safety that is issued for industrial

accidents effects analysis and consequence analysis. Programme was developed by TNO

Built Environment and Geosciences Company – Netherlands and programme models are

based „Yellow Book”, internationally recognised as a standard for risk analysis issuance.

Threshold values (overpressure within shockwave front) used for effect on population,

are the following:

- 0.3 bar – for high mortality area (area I);

- 0.07 bars – for irreversible injuries area (area II).

Threshold values define areas where life (area I) respectively population health (area

II) may be in danger.

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Inputs 30 tone 10 tone 8 toneType of TNT model Based upon mass Based upon mass Based upon massChemical name (YAWS) (YAWS) (YAWS)TNT mass (kg) 30000 10000 8000Equivalency factor (%) 14 14 14Distance from release (Xd) (m) 200 200 200Threshold overpressure (mbar) 70 70 70

Outputs 30 tone 10 tone 8 tonePeak overpressure at Xd (mbar) 115,42 69,002 62,162Equivalent TNT mass (kg) 4200 1400 1120

Damage (general description) at Xd Minor damage (Zone D: 3.5 -

17 kPa).Minor damage (Zone

D: 3.5 - 17 kPa).Minor damage (Zone

D: 3.5 - 17 kPa).

Damage to brick houses at Xd

Not habitable without major repair works. Partial roof

failures, 25% of all brick walls have failed, serious damage to

the remaining carrying elements. Damage to

windowframes and doors (7-15 kPa).

Habitable after relatively easy repairs. Minor

structural damage (3 kPa).

Habitable after relatively easy repairs. Minor

structural damage (3 kPa).

Damage to structures (empirical) at Xd

Minor damage to steel frames (8-10 kPa). Connections

between steel or aluminium ondulated plates have failed 7-14 kPa). The roof of a storage

tank has collapsed (7 kPa).



Damage to windows (houses before 1975) at Xd (%)

99,788 96,16 93,925

Damage to windows (houses after 1975) at Xd (%)

98,146 78,339 69,844

Confined mass in explosive range (kg)

30000 10000 8000

Dist. center mass of confined expl. cloud to study point (m)

200 200 200

Dist. center mass of cloud at threshold overpressure (m)

285,85 198,19 183,99

In Figure 4.21 is presented overpressure depending on distance for case i. One

quantity of 30 t quantity of ammonium nitrate.

Figure 4.21 Overpressure depending on distance – 30 NA tonnes

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30 tone

Distance from center mass of explosive cloud [m]300250200150100500

Ove

rpre

ssu

re [

mb

ar]

6.000

5.500

5.000

4.500

4.000

3.500

3.000

2.500

2.000

1.500

1.000

500

0

Simulation calculations show that high mortality area (Area I with overpressure above

300 m bars) is within a cycle with a radius of 106.5 m and irreversible area (Area II with

overpressure above 70 m bars) is within a circle with a radius of 285.85 m.

If we take into consideration that this hypothetical explosion produces indoors of one

of the explosive storage yards chamber, there results that effects will be felt only by persons

eventually present within the affected storage chamber.

In Figure 4.22 there is presented overpressure depending on distance for cases ii.

Explosion of one quantity of 10 t ammonium nitrate.

Figure 4.22. Overpressure depending on distance – 10 tonnes NA

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10 tone


Ove

rpre

ssu

re [m

ba

r]

6.000

5.500

5.000

4.500

4.000

3.500

3.000

2.500

2.000

1.500

1.000

500

0

High mortality area (Area I with an overpressure above 300 m bars) is within a circle

with a radius of 74 m and the irreversible injuries area (Area II with an overpressure above 70

m bars) is within a cycle with a radius of 198.2 m.

In this case we have considered that the accident produces even on discharge ramp

situated immediately near explosive underground storage yard. In figure 4.23 there is

presented the map with area of risk associated to this scenario.

Figure 4.23 Map with risk areas representation

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To observe that area 1 includes exterior enclosure of explosives storage yard but also a

part of the connection road between open pit and ore stockpile.

In Figure E 4.24 there is presented overpressure depending on distance for case iii.

Explosion of one quantity of 8 t ammonium nitrate.

Figure 4.24 Overpressure depending on distance – 8 tons NA

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8 tone


Ove

rpre

ssu

re [

mb

ar]

6.000

5.500

5.000

4.500

4.000

3.500

3.000

2.500

2.000

1.500

1.000

500

0

High mortality area (Area I with overpressure above 300 m bars) is within one circle

with a radius of 68 m and irreversible injuries area (Area II with an overpressure above 70 m

bars) is within one circle with a radius of 184 m.

In this case we have considered that accident produces within area where the road

crossed by the explosive truck towards the open pit passes through enclosure that contains

maintenance and reparations workshop for equipments from the open pit that is the only

objective with a higher sensitivity along all route. In figure 4.25 there is presented the map

with representation of risk areas associate to this scenario.

Figure 4.25. Map with risk areas representation

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We note that such kind of accident can affect a large part of the personnel within the

area because reparation works for very large equipments are usually carried out outside the

buildings.

2.5 Risks associated to tailings management facilities

The quantitative risk assessment of the tailings dams has emphasized that, the biggest

risk is associated to braking through the dam body, which can lead to uncontrolled loss into

the environment of the contained water and of a part of the tailings.

Careful quantification of risk needs setting possibilities of occurrence of some

damages that cause uncontrolled loss of pond content, as well as consequences measure

assessment of such events. Quantification process is difficult and many times vague, due to

data base insufficiency and to definition difficulty of some measurement unities for

consequences. In order to overcome this shortcoming it can use risk empirical assessment and

of its components through indicators proportional to risk. Within this method pond is regarded

as a system. Pond components that have implication into triggering of some disposal

mechanisms are identified, on the basis of adverse event trees. Measure where damage or

inconsistency with given specifications of one component can contribute to pong breaking

through is characterized through a gravity indicator IG:

IG = CM . PC . DC

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where: -CM is a partial indicator that expresses component damage share into

breakage triggering process;

-PC – partial indicator that expresses component damage probability;

-DC – partial indicator that expresses the extent to which component damage

can be detected in advance.

Each partial indicator is appreciated on a scale of 1 to 5. Maximum value of gravity

indicator IG = 125 corresponds to component the damage of which or inconsistency with

specifications has an extremely important effect in one failure mechanism triggering (CM =

5), the failure of which (or deviation from safety conditions) is very probable (PC = 5) and as

well is very hard to be detected in advance (DC = 5).

Components identified as being potentially initiators of a breakthrough were: guard,

beach, downstream slopes, material granulometry, decant water collection system, drainage,

collected water discharge. Partial indicators have been determined through consultations and

successive mediations achieved by the specialists involved into study elaboration. As a result,

for example, that freeboard non-compliance leads almost certainly to dam breakage (CM = 5)

and that probability of occurrence of such a situation is average (PC = 3) but that situation

detection is easily made (DC = 1). As regards decanted water collecting system, its failure

leads almost certainly to pond breakage through lack of control of accumulated water (CM =

5), failure probability is average (PC = 3) and detection in advance, that allow useful

interventions is easy enough (DC = 2). Similarly, there were established the indicators for

other components also. Synthesis is presented in table 4.26.

Table no. 4.26 Determined partial indicators synthesis

Parameter or component CM PC DC IG=CM⋅PC⋅DC

Guard

Beach width

Downstream slopes

Material quality in dam body (permeability,

stability)

Decanted water discharge system

Discharge system

5

4

5

3

5

3

3

3

2

2

3

3

1

1

1

2

2

3

15

12

10

12

30

27

From this assessment it results the necessary hierarchy of safety increasing measures.

As it can be observed, decanted water collection system has maximum gravity indicator. In

the same priority order enters also establishment of periodical control of diversion and

draining gallery status. Then follows, in gravity indicator order, operational parameters

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package (freeboard, beach, dam body material quality, slopes) that needs careful monitoring

through an adequate system and control through operation measures.

Sudden and uncontrolled loss of tailings pond content can have the following

categories of consequences:

- casualties;

- effects on biological and physical environment;

- material damages brought to third parties from the affected area;

- damages brought to Deva Gold, through reparation works and through

production interruption during remedial trials;

- effects on company image (traded, permit system, etc.).

Quantification of these consequences is very difficult due to the fact that some

consequence do not have a money expression, the way human life loss have, and others are

extremely hard to assess in monetary units, as for example effects on environment or effects

on company image. Human settlements are situated relatively far away from the dam and thus

loss of human lives are unlikely. Effects on environment and on properties are possible but

delimited especially because of reduced porosity of the material stored within this pond, and

damages produced to company and its impaired image in case of an accident will produce

almost certainly.

Area possible to be affected, in the unlikely situation of dam failure would include,

until Mures confluence, villages Hondol (598 population) and Certeju de Sus (1795

population) belonging to joint village Certejul de Sus, as well as village (529 population)

including Hărău joint village.

After filed investigations, floods type ‘’flash-flood’’ and/or,,mud-flood’’ that

could result after tailings pond failure could be eventually affected approximately 50

household from Hondol area, 40 from Certeju de Sus and about 80 from Bârsău village, a

series of socio-economical objectives (emplacement SC MINVEST SA from Certeju de Sus,

General School from Hondol) as well as a significant surface of arable fields downstream

Certeju de Sus area. In figure 4.27. there is presented the map with possible affected areas

figure.

Figure 4.27 Map with possible floods affected areas

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A positive influence in case of such an accident (flood regularization, stopping of one

quantity of sterile) could exert to meadows developed within riverbed Măcriş and its

neighbourhood, downstream of proposed tailings dam, consisting of quite vigorous specimens

of Alnus glutinosa, Salix caprea, Carpinus betulus, Fraxinus excelsior etc., that produces an

appreciable density in that area.

Critical areas identified after investigations are the centre of Hondol village within the

location where Hondol river crosses the road DJ 761 and most part of Barsau village centre

developed on the left side of the Certej river. To be mentioned the fact that objectives from

the above mentioned villages are not protected by embankments or regularization works ,

streams being only arranged on some sectors through recalibration and rectification works

(Certeju de Sus, Bârsău streams); it is intended to increase the flow-rate/speed of the water

discharged and to decrease the level of the same flow in order to limit overflowing.

Quantitative assessment of risks associated to tailings pond makes the object of some

separate studies carried out by UTCB Bucharest, namely:

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- „Risk study regarding dam failure’ ;

- „Pollutants dispersion on surface water course Certej – Mureş – Tisa – Dunube” ;

- „Analysis through modelling of migration of potential effects and of possible

accidents consequences’.

C. Equipment description and measures used for installations safety

In order to avoid occurrence of some events susceptible to trigger a major accident,

each employee can fulfil work attributions, only after he was trained and has duly endorsed

the following:

- company internal regulation;

- work instructions specific to the place of work;

- labour protection instructions, for fire protection and civil protection, specific

to work place;

- knowledge of toxic substances characteristics used on work place and of

individual protection equipment and of work necessary to elimination or reduction of the

possible effects of these substances on human body.

- notions of first aid;

Installations within S.C. DEVAGOLD S.A. are designed and carried out in order to

work with toxic and dangerous substances. All equipment are built from material

corresponding to work environment.

Installations are provided with measuring and control apparatus that is maintained and

repaired by specialized personnel. This apparatus is checked by metrology authorized

laboratories.

Oxygen cryogenic tanks have double walls between which space is vacuumed for

temperature maintenance. There are provided safety valves set to working pressure, level

indicator, pressure gauge, system of surveillance of level from the distance and flange (disk)

of breakage.

Liquefied petroleum gas is placed outdoors with a concrete watt, is built from steel and

falls under ISCIR incidence. Is provided with safety valves with arch set on 8 bar pressure,

manometric gauge and glass, manometric thermometers, sectioning valve son inlet and

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outlet routes and safety closing hydraulic system with manual actuating on liquefied

petroleum gas inlet and outlet routes.

Gas tanks are buried and built with double walls in order to avoid ground

pollution in case of breakage and they are provided with manholes and venting pipelines.

In all the installation there is respected maintenance programme for equipments and

measuring and control apparatus.

Any intervention on electrical installations from objects endowment is carried out only

by specialized personnel (electrician).

In order to provide safety operation of installations there are carried out revision works

of these ones on basis of some technological, mechanical, electrical, automation and labour

protection and PSI works.

Necessary interventions and reparation on company objectives are carried out only on

basis of specifically assumptions issued according to legislation in force and based on which

there is disposed and carried out the necessary measures for prevention of any unwanted

events.

Periodically is checked flanges and valves sealing. In the event of leakage observation,

immediate action is taken: product transfusing into another vessel or instant remedial if it is

possible.

There is periodically checked, through non-destructive control, tanks and pipelines

walls thickness. There are carried forward revisions for equipments subject to ISCIR

incidence.

Installations operation is carried out according to Operation Regulations provisions,

existing in each installation. These regulations include, except technological process and

Instructions regarding work on phase and Instructions regarding labour protection, fire

protection and civil protection.

Cyanide storage area is marked and there are prominently displayed alarm indications

for toxic product.

Documents

SECURITY REPORT ,,Gold–silver ore mining of Certej ...apmtm-old.anpm.ro/files/ARPM TIMISOARA/Reglementari/DEVA GOLD - en/Security report...SECURITY REPORT ,,Gold–silver ore mining