Safe Handling ofCompressed Gases in theLaboratory and Plant

Safe Handling ofCompressed Gases in theLaboratory and Plant

Safe Handling of

Compressed Gases in the Laboratory and PlantBefore we are allowed to drive a car, moststates require proof of our ability to drive.To become a proficient and safe driver, onemust have skill, judgment, and drivereducation. We do not always consider thatwe are performing a hazardous operationby driving a car; yet the fact remains thatmany people are killed or hurt every day asa result of carelessness in handling thismachine. Although the safety record of thecompressed gas industry is excellent, thequestions raised by the users of gasproducts, and the accidents involving thesesame users, show that many of them haveneither learned nor applied the safetymeasures that would earn them their“license” for handling compressed gas.When handled by personnel who areproperly trained and aware of the potentialhazards, compressed gases are as safe towork with as most of the ordinary chemicalliquids and solids normally handled on aroutine basis in any laboratory or plant.

A compressed gas is defined by theDepartment of Transportation (DOT) as“any material or mixture which exerts inthe packaging an absolute pressure of280 kPa (40.6 psia) or greater at 20°C(68°F).1”

Hazards

The handling of compressed gases must beconsidered more hazardous than thehandling of liquid and solid materialsbecause of the following properties uniqueto compressed gases: pressure, low flashpoints for flammable gases, low boilingpoints, and no visual and/or odor detectionof many hazardous gases. Hazards mayarise as a result of equipment failure andleakage from systems that are not pressure-tight. Also, improper pressure control maycause over pressurization of a processcomponent, or unsafe reaction rates due topoor flow control. Diffusion of leakinggases may cause rapid contamination of theatmosphere, giving rise to toxicity,anesthetic effects, asphyxiation, and rapidformation of explosive concentrations offlammable gases. The flash point of aflammable gas under pressure is alwayslower than ambient or room temperature.Leaking gas can therefore rapidly form anexplosive mixture with air.

Low-boiling-point materials can causefrostbite on contact with living tissue. Thisis common among the cryogenic liquidssuch as nitrogen and oxygen, but it alsocan result from contact of the liquid phaseof liquefied gases such as carbon dioxide,fluorocarbons, and propylene. Somecompressed gases are similar to otherchemicals in that they are corrosive,irritating, and highly reactive.

The procedures adopted for the safehandling of compressed gases are mainlycentered on containment of the material,to prevent its escape to the atmosphere,and proper control of pressure and flow.All rules and regulations are directedtoward these ends. Emergency proceduresare usually only necessary because a basicrule of handling has been broken. It is farbetter to observe the rules and avoid theneed for emergency measures. A listing ofsome common violations of basic rules forhandling compressed gases is given inTable 1.

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Safe Handling of

Compressed Gases in the Laboratory and Plant

General Precautions

Some general precautions for handling,storing, and using compressed gasesfollow.2, 3, 4

1. Never drop cylinders or permit them tostrike each other violently.

2. Cylinders may be stored in the open,but should be protected from theground beneath to prevent rusting.Cylinders may be stored in the sun,except in localities where extremetemperatures prevail; in the case ofcertain gases, the supplier’srecommendation for shading should beobserved. If ice or snow accumulateson a cylinder, thaw at roomtemperature.

3. The valve-protection cap should be lefton each cylinder until it has beensecured against a wall or bench, orplaced in a cylinder stand, and is readyto be used.

4. Avoid dragging, rolling, or slidingcylinders, even for a short distance.They should be moved by using asuitable hand truck.

5. Never tamper with pressure reliefdevices in valves or cylinders.

6. Do not store full and empty cylinderstogether.

7. Do not have full and empty cylindersconnected to the same manifold.Reverse flow can occur when an emptycylinder is attached to a pressurizedsystem.

8. No part of a cylinder should besubjected to a temperature higher than125°F. A flame should never bepermitted to come in contact with anypart of a compressed gas cylinder.

9. Cylinders should not be subjected toartificially created low temperatures(-40°F or lower), since many types ofsteel will lose their ductility and impactstrength at low temperatures. Specialstainless steel cylinders are availablefor low temperature use.

10. Do not place cylinders where they maybecome part of an electric circuit.When electric arc-welding, precautionsmust be taken to prevent striking anarc against a cylinder.

11. Bond and ground all cylinders, lines,and equipment used with flammablecompressed gases.

12. Use compressed gases only in a well-ventilated area. Toxic, flammable, andcorrosive gases should be carefullyhandled in a hood. Propercontainment systems should be usedand minimum quantities of theseproducts should be kept on-site.

13. Cylinders should be used in rotation asreceived from the supplier. Storageareas should be set up to permit properinventory rotation.

Table 1

1. Unsecured cylinders2. Cylinders stored without protective caps3. Noncompatible gases (such ashydrogen and oxygen) stored together

4. Cylinder valves open when cylinder isnot in use (an attached regulator with aclosed discharge valve is not sufficient)

5. Fire extinguishers not present duringwelding, burning, or brazing operations

6. No safety showers and eyewashfountains where corrosive gases areused

7. No gas masks and/or self-containedbreathing apparatus convenientlylocated near areas where toxic gasesare used or stored

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Common OSHA ViolationsInvolving Compressed Gas

14. When discharging gas into a liquid, atrap or suitable check valve should beused to prevent liquid from gettingback into the cylinder or regulator.

15. When using compressed gases, wearappropriate protective equipment, suchas safety goggles or face shield, rubbergloves, and safety shoes. Well-ventilated barricades should be used inextremely hazardous operations, suchas in the handling of fluorine. Gasmasks should be kept available forimmediate use when working withtoxic gases. These masks should beplaced in convenient locations in areasnot likely to become contaminated, andshould be approved by the U.S. Bureauof Mines for the service intended.Those involved in the handling ofcompressed gases should becomefamiliar with the proper applicationand limitations of the various types ofmasks and respiration aids available.

16. When returning empty cylinders, closethe valve before shipment, leavingsome positive pressure in the cylinder.Replace any valve outlet and protectivecaps originally shipped with thecylinder. Mark or label the cylinder“empty” (or utilize standard DOT“empty” labels) and store in adesignated area for return to thesupplier.

17. Before using cylinders, read all labelinformation and Safety Data Sheets(SDS) associated with the gas beingused. Observe all applicable safetypractices.

18. Eye baths, safety showers, gas masks,respirators, and/or resuscitators shouldbe located nearby but out of theimmediate area that is likely to becomecontaminated in the event of a largerelease of gas.

19. Fire extinguishers, preferably of thedry chemical type, should be kept closeat hand and should be checkedperiodically to ensure their properoperation.

20. Carefully review the pressure rating ofeach component in the gas stream.The regulator outlet pressure may notexceed the component with the lowestpressure rating. A pressure relief valveset below the lowest componentpressure is recommended.

The user of compressed gases shouldbecome familiar with the first-aid methodsto be employed in cases of overexposure orburns caused by a gas. A plant doctorshould be familiar with whatever furthertreatments may be necessary. Unnecessarydelay in the treatment of a patientovercome by a toxic gas or burned by acorrosive gas could cause the patientpermanent damage, and might even resultin death. Authorized personnel shouldadminister first aid; however, they shouldnot take it upon themselves to administermedical treatments. A physician should becontacted immediately.

Cylinders

Figure 1 Cylinder parts and markings.

The supplier seeks to assure the safety ofcylinders through adherence to regulationsset forth by the Department ofTransportation, and by supplying cylinderswith specific valves, labels, and/or markingsin accordance with recognized standards.

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It is mandatory for the supplier to shipcylinders manufactured in conformancewith DOT regulations and to follow DOTregulations in the testing and inspection ofcylinders, the proper filling of thesecylinders, and the use of pressure reliefdevices that are approved by the DOT.

Figure 1 shows cylinder parts andimportant cylinder markings. The cylindercap (1) protects the cylinder valve. Thevalve handwheel (2) is used to open andclose the cylinder valve. Valves areoccasionally not equipped withhandwheels, and require special wrenchesto effect operation. The valve packing nut(3) contains a packing gland and packingaround the stem. It should not betampered with when used in conjunctionwith diaphragm-type valves. A pressurerelief device (4) permits gas to escape ifincreased unsafe pressures are attained.The valve outlet connection (5) connects topressure and/or flow-regulatingequipment. Various types of connectionsare provided to prevent interchange ofequipment for incompatible gases, usuallyidentified by CGA (Compressed GasAssociation) number; for example, CGA No.350 is used for hydrogen service. Acylinder collar (6) holds the cylinder cap atall times, except when regulatingequipment is attached to the cylindervalve. The valve outlet cap (7) protectsvalve threads from damage and keeps theoutlet clean; it is not used universally.

Specification number (8) signifies that thecylinder conforms to the Department ofTransportation specification DOT-3AA,governing materials of construction,capacities, and test procedures, and thatthe service pressure for which the cylinderis designed is 2265 psig at 70°F.

The cylinder serial number is indicated by(9), and (10) indicates the date (month andyear: in this case, October 2010) of initialhydrostatic testing. Thereafter, hydrostaticpressure tests are performed on cylinders,for most gases, every 5 years to determine

their fitness for further use. At this timenew test dates are stamped into theshoulder of the cylinder. Presentregulations permit visual test in lieu ofhydrostatic tests for low-pressure cylindersin certain gases free of corrosive agents;regulations also allow for hydrostaticpressure tests at 10-year intervals forcylinders in high-pressure service forcertain gases. The original inspector’sinsignia for conducting hydrostatic andother required tests to approve the cylinderunder DOT specifications is shown by (11).

Filling

Nonliquefied gases may be filled to theservice pressure marked on a cylinder.These markings will appear on theshoulder of the cylinder, i.e., DOT3AA-2265, indicating that the cylinder has beenmanufactured in accordance with DOTspecifications 3AA, and the cylinder fillingpressure is 2265 psi at 70°F. At present,DOT regulations permit a 110% filling forcertain non-liquefied, non-flammablegases. Liquefied gases, on the other hand,must be filled to a filling density. Thisfilling density represents the maximumweight of the material permitted in thecylinder, as a percentage of the watercapacity of the cylinder.

Since compressed gas cylinders arehandled by a number of different types ofplant personnel, consider the precautionsto be taken in handling from the time it isdelivered until the time it is emptied andready for return.

Receipt and Content Identification

When a cylinder is delivered to thereceiving department, it should have1) content identification by stenciling orlabels, 2) a DOT label, and 3) a valve-protection cap. Under no circumstancesshould the means of identification beremoved from the cylinder. The valve-protection cap (Figure 1) should alsoremain in place until the user has secured

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the cylinder and is ready to withdraw thecontents. DOT labels are required forcylinders in interstate transportation.Some states require these labels forintrastate shipments also. These labelshave a minimum of precautionary handlinginformation and will classify the cylindercontents as flammable, nonflammable,poison, or corrosive.

Proper identification of cylinder content canbe made by checking the cylinder shoulderlabel. Stenciling and/or cylinder color shouldnever be used for positive identification. Ifany doubt exists as to cylinder content,contact your supplier before using thecylinder.

Proper Storage

After cylinders are received, they should bestored in a detached and well-ventilated oropen-sided building. Storage buildings orareas should be fire resistant, wellventilated, located away from sources ofignition or excessive heat, and dry. Suchareas should be prominently posted withthe names of the gases being stored.Indoor storage areas should not be locatednear boilers, steam or hot water pipes, orany sources of ignition. Outdoor storageareas should have the proper drainage andshould be protected from the direct rays ofthe sun in localities where hightemperatures prevail. Subsurface storageareas should be avoided. Cylinders shouldbe protected against tampering byunauthorized personnel.

Cylinders should be stored in accordancewith CGA Pamphlet P-1. Where gases ofdifferent types are stored at the samelocation, cylinders should be grouped bytypes of gas, the groups arranged to takeinto account the gases contained -- forexample, flammable gases should not bestored near oxidizing gases. Storage in alaboratory should be confined to only thosecylinders in use. In all cases, storage areasshould comply with federal, state, and local

requirements as well as with the standardsof the Compressed Gas Association and theNational Fire Protection Association.2,4

Transportation

When cylinders are being moved from astorage area into the laboratory or plant,the valve-protection cap should be left inplace. The cylinder should then betransported by means of a suitable handtruck (Figure 2). Such a hand truckshould be provided with a chain or belt forsecuring the cylinder on the truck. If alarge number of cylinders must be movedfrom one area to another, a power device,such as a fork truck equipped with a specialcontainer and provided with some meansof securing the cylinder, can be used. Donot lift cylinders by the cap. Avoiddragging or sliding cylinders. Use handtrucks even for short distances.

Securing Cylinder Prior to Use

When the cylinder has reached itsdestination in the laboratory or plant, itshould be secured to a wall, a bench, orsome other firm support, or placed in acylinder stand, rack or cabinet (Figures 3-9). An ordinary chain or belt of the typecommonly available from your gas suppliercan be used. Once the cylinder has beensecured, the cap may be removed, exposingthe valve. The number of cylinders in alaboratory should be limited to minimizethe fire and toxicity hazards.

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Figure 2 – Models 6114A and 6214ACylinder Hand Trucks

Pressure Relief Devices

Pressure relief devices are incorporated inmost DOT compressed gas cylinders, exceptthose containing poison or toxic gas, wherethe risk of exposure to fumes is consideredmore hazardous than that of a potentialcylinder failure. Pressure relief devices areincorporated in the cylinder valve, in plugsin the cylinder itself, or both. In certaintypes of gas service, and in many cylindersover a particular length (usually 65”), twopressure relief devices may be required, oneat each end of the cylinder.

Pressure relief devices are required to meetDOT regulations.5 These pressure reliefdevices are of four basic types:

1. Spring-loaded pressure relief valve, usedmostly for low-pressure, liquefied,flammable gases.

2. Frangible disc, used mostly for high-pressure cylinders.

3. Frangible disc backed up by a fusiblemetal for non-liquefied, flammablegases and some liquefied gases such ashydrogen, carbon monoxide, andhydrogen chloride.

4. Fusible metal for certain toxic, corrosivegases such as chlorine and sulfurdioxide.

The spring-loaded pressure relief valveconsists of a spring-loaded seat that opensto relieve excessively high pressures andthen closes when the pressure returns to asafe value.

The frangible disc will burst at a pressurethat is above the service pressure of thecylinder, but usually not higher than thetest pressure for that cylinder.

The frangible disc backed up by a fusiblemetal will function only if there is thepresence of excess pressure which causesthe disc to burst, and high temperaturewhich causes the fusible metal to melt.The release of the cylinder contents isdependent upon both pressure andtemperature. 7

Figure 3 – Model 708 BenchType Cylinder Holder

Figure 4 – Model 710 WallMounted Cylinder Holder

Figure 5 – Model 700 and 701Small Cylinder Stands

Figure 6 – Model 704-BLecture Bottle Holder for

Bench Use

Figure 7 – Model 704-WLecture Bottle Holder for

Wall Mounting

Figure 8 – Model 1191 LectureBottle Storage Cabinet

Figure 9 – Model 6530 SeriesCylinder Storage Racks

The fusible metal devices melt at excessivetemperatures (either 165°F or 212°F),allowing the entire contents of the cylinderto escape.

Pressure relief devices will prevent acharged cylinder from bursting due toexcessively high temperatures or pressures.However, devices 3 and 4 will not prevent acharged cylinder from bursting solely, as aresult of over pressurization. A temperaturein excess of the melting point of the fusiblemetal is required for release of the product.Since the proper functioning of cylinderpressure relief devices depends to a largeextent on the proper filling of a cylinder,such filling should never be attempted bythe user. Pressure relief devices may alsofail to function properly if an intense flameimpinging on the side wall of a cylinderweakens the metal to the point of failurebefore heat or pressure can cause thepressure relief device to function properly.

Finally, it must be emphasized thattampering with cylinder pressure reliefdevices is extremely hazardous.

Knowing the Gas to be Handled

It is of the utmost importance that the userbe well aware of those properties of acompressed gas that represent hazards(such as flammability, toxicity, chemicalactivity, and corrosive effects). Everyattempt should be made to learn thesevarious properties before the gas is put touse. It is sometimes difficult to determinethe major hazard of any one gas, since thisfactor is influenced a great deal by how thegas is used. In a laboratory hood in thepresence of an open flame, the flammabilityof carbon monoxide might well be themajor hazard, whereas in a pilot-plant runusing carbon monoxide as a reactant,leakage, and therefore toxicity, mayrepresent the major hazard.

Figure 10 shows the flammability ranges ofvarious gases.6 Although the flammability

ranges of liquefied petroleum gases such asbutane and propane are relatively short,only very small concentrations arenecessary to create flammable mixtures.The flammability ranges of acetylene,carbon monoxide, ethylene oxide, hydrogensulfide, and hydrogen are extremely long,indicating that they can form explosivemixtures with air under a wide variety ofconditions.

It is important to know what materials ofconstruction must be used with a gas toprevent failure of equipment due tocorrosion, or to avoid possible formation ofhazardous compounds (such as acetylidesformed by the reaction of copper withacetylene or gases containing acetylene asan impurity) or the possible formation offulminates when mercury is used in thepresence of ammonia.

The hazards of toxic, flammable, andcorrosive gases can be minimized byworking in well-ventilated areas. Wherepossible, work should be done in a hood,employing cylinder sizes that will assureuse of all the gas within a reasonableamount of time. Leaks should not beallowed to go unchecked. Advise the

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Figure 10 – Flammability Range of Gases

supplier immediately of cylinder leaks thatcannot be stopped by simple adjustment,such as tightening a packing nut.

Proper Discharge of CylinderContents

For controlled removal of the liquid phaseof a liquefied gas, a manual control is used(Figure 11). Special liquid flow regulatorsare also available. It must be rememberedthat withdrawal of liquid must necessarilybe carried out at the vapor pressure of thematerial. Any attempt to reduce thepressure will result in flashing of all orpart of the liquid to the gas phase.

Rapid removal of the gas phase from aliquefied gas may cause the liquid to cooltoo rapidly, causing the pressure and flowto drop below the required level. In suchcases, cylinders may be heated in a waterbath with temperature controlled to nohigher than 125°F. Rapid gas removal canalso be effected by transferring the liquidto a heat-exchanger, where the liquid isvaporized to a gas. This method imposesno temperature limitations on thematerial; however, care should be taken toprevent blockage of the gas linedownstream of the heat-exchanger, as thismay cause excessive pressure to build up inboth the heat-exchanger and the cylinder.Safety relief devices should be installed inall liquid-transfer lines to relieve sudden,dangerous hydrostatic or vapor-pressurebuildups.

For nonliquefied gases, the most common

device used to reduce pressure to a safevalue for gas removal is a pressureregulator. This device is shown inFigure 12. It consists of a spring -(or gas-) loaded diaphragm that controlsthe throttling of an orifice. Deliverypressure will exactly balance the deliverypressure spring to give a relativelyconstant delivery pressure. Review thepressure rating of all components in thegas stream and confirm that the regulatoroutlet pressure does not exceed anycomponent.

Pressure Regulator Handling and Use

A regulator should be attached to acylinder without forcing the threads. Ifthe inlet of a regulator does not fit thecylinder outlet, no effort should be madeto try to force the fitting. A poor fit mayindicate that the regulator is not intendedfor use on the gas chosen.

The following procedure should be used toobtain the required delivery pressure:

1. After the regulator has been attached tothe cylinder valve outlet, turn thedelivery pressure-adjusting screwcounterclockwise until it turns freely.

2. Open the cylinder valve slowly until thetank gauge on the regulator registersthe cylinder pressure. At this point, thecylinder pressure should be checked tosee if it is at the expected value.Contact your gas supplier if pressure isless than expected. (Note: Low cylinderpressure may indicate a leaking valvewhich can be a serious safety issue.)

Figure 11 – Model 4351 Manual Control Valve

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Figure 12 – Model 3120A Dual Stage High Purity Brass Regulator

3. With the flow-control valve at theregulator outlet closed, turn thedelivery pressure-adjusting screwclockwise until the required deliverypressure is reached. Control of flow canbe regulated by means of the valvesupplied in the regulator outlet or by asupplementary valve put in a pipelinedownstream from the regulator. Theregulator itself should not be used as aflow control by adjusting the pressureto obtain different flow rates. Thisdefeats the purpose of the pressureregulator, and in some cases wherehigher flows are obtained in thismanner, the pressure setting may be inexcess of the design pressure of thesystem.

4. After flow is established, the set deliverypressure may decrease slightly. Checkto see that the delivery pressure is asdesired and make any necessaryadjustments.

5. Ensure that the delivery pressure doesnot exceed the pressure rating of anycomponent in the gas stream.

Types of Pressure Regulators

The proper choice of a regulator dependson the delivery-pressure range required,the degree of accuracy of delivery pressureto be maintained, and the flow raterequired. There are two basic types ofpressure regulators, single-stage anddouble, or two-stage. The single-stage typewill show a slight variation in deliverypressure as the cylinder pressure drops. Itwill also show a greater drop in deliverypressure than a two-stage regulator as theflow rate is increased. In addition, it willshow a higher “lock up” pressure (pressureincrease above the delivery set-pointnecessary to stop flow) than the two-stageregulator. In general, the two-stageregulator will deliver a more nearlyconstant pressure under more stringentoperating conditions than will the single-stage regulator.

Gas purity will also need to be consideredwhen selecting the correct regulator.Regulator design and materials ofconstruction could adversely affect thepurity of the gas being used. Choose aHigh Purity Regulator for applicationswhere purity of gas is critical. For moredetails and information on high puritydesigns, reference your MATHESONCatalog or contact your specialty gasrepresentative.

Manual Flow Controls

Where intermittent flow control is neededand an operator will be present at all times,a manual type of flow control may be used.This type of control (illustrated in Figure11) is simply a valve that is operatedmanually to deliver the proper amount ofgas. Fine flow control can be obtained, butit must be remembered that dangerouspressures can build up in a closed systemor in one that becomes plugged, since nomeans are provided for automaticprevention of excessive pressures.

Determining the Amount of Gasin a Cylinder

As the content of a cylinder of nonliquefiedgas is discharged, the cylinder pressuredecreases by an amount proportional to theamount withdrawn. The cylinder shouldbe considered empty while positivepressure (25 psig or greater) still remains,in order to prevent reverse flow andcontamination. Failure to close the valveon an empty cylinder will allow air andmoisture to be drawn into the cylinder as it“breathes” during temperature changes; anexplosive mixture may build up if the gas isflammable; and an extremely corrosivecondition will be created in cylinders thatcontain chlorine, hydrogen chloride, orother acid-forming or corrosive gases.

As the vapor phase of a liquefied gas iswithdrawn from a cylinder, the cylinderpressure or vapor pressure will remainconstant as long as any liquid is present.

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This condition holds true if thetemperature does not vary. If, however, thematerial is withdrawn from the cylinder ata rapid rate, the material itself will supplythe heat for vaporization, and uponsubsequent cooling, the vapor pressure willbe lowered. It is, therefore, impossible todetermine the content of a cylindercontaining a liquefied gas, except byweighing. A scale such as the one shownin Figure 13 makes this convenient.Cylinders containing liquefied gases arestamped or tagged with the tare weight inorder to allow the content to bedetermined.

An indication of cylinder-content depletionfor some high pressure liquefied gases suchas carbon dioxide, ethane, and nitrousoxide can be obtained by noting thecylinder pressure. After depletion of theliquid phase, the cylinder pressure willdecrease below the normal vapor pressure,as long as the contents have not beenwithdrawn rapidly before the cylinderpressure is noted. A cylinder containingcarbon dioxide will have approximately20% of its original content remaining afterdepletion of the liquid phase. As withcylinders of nonliquefied gases, cylinderscontaining liquefied gases should never becompletely emptied, in order to preventreverse flow and contamination of thecylinder.

Handling Empty Cylinders

Where cylinders are considered empty, thevalves should be closed. Valve-protectioncaps, outlet dust caps, and other

accessories shipped with the cylindershould be attached to the cylinder asreceived. The cylinder should be markedor labeled “empty.” Cylinders should thenbe placed in a proper storage area,segregated from full cylinders, to awaitpickup for return to the supplier.

Carelessness in the handling of an emptycylinder could result in its being mistakenfor a full cylinder. Connecting an emptycylinder to a high-pressure system couldcause foreign materials to back up into thecylinder, resulting in all the attendanthazards of reverse flow, and possible violentreaction within the cylinder.

Leak Detection

Check cylindersand all connectionsunder pressure forleaks prior to usingthe contents.When using toxicgases, it isadvisable that somedevice be used towarn of thepresence of toxicconcentrations.

There arenumerousmonitoring devices available for detectionof dangerous concentrations of gases in theatmosphere (Figure 14). There are alsoappropriate chemical procedures fordetecting leaks in lines and equipment andfor determining dangerous concentrationsof gases in the atmosphere. The user ofgases should become familiar with suitablecontrol procedures for the determinationof such dangerous concentrations.Instructions are usually supplied in theSafety Data Sheets (SDS) associated withthe particular gas being used. SDS sheetscan be found atwww.chemadvisor.com/MATHESON

Figure 14 - Model 8081AToxic Gas Leak Detector

Figure 13 – Model DS-R Electronic Cylinder Scales

An emergency plan can function efficientlyonly if a trained safety crew is educated inthe proper handling of gas cylinders, withtraining in the procedures to be followed incases of emergency with all the gaseshandled by the facility. Equipment such asself-contained gas masks must be availablefor handling toxic gases or for handlingasphyxiating gases in close confines.Emergencies involving flammable gasesmust be managed with the utmost care inorder to prevent ignition. The aftermath ofgross leakage is extremely important. Allareas must be adequately vented before therestoration of power in cases of flammable-gas leakage. Areas contaminated bycorrosive gases must be adequately ventedand completely washed down to preventsubsequent degradation of delicateinstruments, electrical contacts, etc.

On rare occasions, emergency action maybe necessary in order to move a leakingcylinder to a location where it can ventsafely, or it may have to be removed from abuilding and brought outdoors. In suchinstances, an emergency plan should beput into effect:

1. Properly warn all personnel required toevacuate a building or section of abuilding.

2. Shut off electrical power to preventignition of a leaking flammable gas.

3. Determine the shortest route to thepoint of gas disposal.

4. Obtain satisfactory conveyance, such asa hand truck, to move the cylinderswiftly.

5. Post the area where the cylinder isventing to prevent tampering byunauthorized personnel.

Handling of Corrosive Gases

Corrosive gases should be stored for theshortest possible periods before use,preferably less than three months. Storageareas should be as dry as possible. A goodsupply of water should be available tohandle emergency leaks. Most corrosivegases can be absorbed in water.

Corrosive gases should not be stored inareas containing instruments or otherdevices sensitive to corrosion. These gasesshould be segregated as to type, androtated so that the oldest stock is usedfirst. Toxic, flammable and corrosive gasesshould be handled carefully. Propercontainment systems should be used andminimum quantities of these productsshould be kept on-site. Cylinders used andthen put back in storage should have allappurtenances (regulators, control valves,etc.) removed from the valve outlet andshould preferably be flushed with drynitrogen or air to keep them in goodworking order.

When corrosive gases are being used, thecylinder valve stem should be periodicallyopened and closed to prevent “freezing.”The valve should be closed when thecylinder is not in use. Regulators andvalves should be closed when the cylinderis not in use and flushed with dry air ornitrogen after use. Such control devicesshould not be left on a cylinder, exceptwhen it is in frequent use. When corrosivegases are to be discharged into a liquid, atrap, check valve, or vacuum break deviceshould always be employed to preventdangerous reverse flow.

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Other Safety Ideas fromMATHESON

The Use of Flash Arrestors

Whenever a flammable gas is to be used itis recommended that a simple flasharrestor be installed in the line. Flashbackis the reversing of the flame such that ittravels through the line back into thepressure regulator or cylinder. Mostwelders incorporate flash arrestors in theirsystem.

Laboratories, however, often use gases likeacetylene, one of the most hazardous, foratomic absorption instruments...and do notincorporate a flash arrestor. The same istrue for other instrumentation such asflame ionization detector GC and flamephotometers. Flash arrestors are easy toinstall in existing systems. They areavailable in either brass or stainless steel.

Heavy Duty HandTrucks

When transportingcylinders, one or two,we recommend the useof heavy duty handtrucks. The handtrucks that we proposeare specifically designedto handle compressedgas cylinders and transport them safelyover all types of surfaces, even gravel beds.

The wheels aredesignated “hi-loadcapacity” and there isa rigid rear carriagesupport whichsupports the weight ofthe cylinders tobalance the truck andcylinder, so you canconcentrate onsteering.

A less specific truck may not encompasssuch features and will lack the necessarystability for cylinder transport.

Gas Detection

Where toxic gases are in constant orintermittent use, it is recommended thatsome sort of toxic gas detector system isused. A continuous monitoring systembased on a GC principle is frequently idealfor a plant which uses benzene or vinylchloride all the time. If the use of toxic gasis intermittent, we recommend theMATHESON-Kitagawa Toxic Gas DetectorSystem.

This systemconsists of asmall,calibrated,100cc handpump. A tubefor a specificvapor isinserted and

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Model 6214A TwoCylinder Hand Truck

Model 8014KB Toxic Gas Detector Tube System

Model 6114A SingleCylinder Hand Truck

Kitagawa Toxic Gas Detector Tubes

Model 6103A Series Flash Arrestor

a sample of the atmosphere is drawnthrough the tube by the pump. In mostcases, a constant color stain is producedwhich varies in length according to theconcentration of the vapor being measured.The system measures over 100 differentmaterials such as ammonia, benzene,chlorine, ethylene oxide, hydrogen sulfide,etc. It is designed for operation bynontechnical personnel.

MATHESON GasCabinets

Many industries haverecognized gascylinder cabinets as acost effective way ofprotecting life andproperty from toxic,flammable andcorrosive gases. Gascabinets can also helpthe user comply withbuilding and fire codesspecified by federal,state and localagencies.

MATHESON’s line of gas cabinets offersmany advantages to users:

• Compliance with Article 80 of theUniform Fire Code, OSHA and NFPAstandards.

• Separate access panel and wire-reinforcedsafety glass viewing window provideadded protection for employees workingwith hazardous gases in the cabinet.

• Fire sprinkler head for extra protection.

• Low-profile cylinder deck makes cylinderinstallation and removal easy.

• Constructed of rugged 12-gauge coldrolled steel with welded seams.

• Cabinets are fitted with u-channelsupports for easy installation andadjustment of many types of gashandling systems.

Excess Flow Valves

The excess flow valve is designed to shutdown gas supply systems in the event ofabnormal flow conditions caused byrupture, fire, open freeflowing valves, etc.The valve willautomatically detectexcess flow when theevent occurs and willshut down the supplyflow immediately sothat the remainingcontent of thecylinder(s) does notempty into the work orstorage area. This is critical with toxic,poisonous or flammable gases but can alsobe important when dealing with inert gasesin small, poorly ventilated areas whereasphyxiation can be a potential hazard.Excess flow valves are highly effective andimportant safety equipment -- MATHESONrecommends these devices whereverhazardous gases are being used.

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Model 1170 Series GasCylinder Cabinet

Model 6290 SeriesExcess Flow Valve

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References

1. Hazardous Materials Regulations of the Department of Transportation, 49CFR Parts 171-180,R. M. Graziano Tariff, issued by R.M. Graziano, Agent, 1920 “L” St. N.W., Washington, D.C. 20036

2. Handbook of Compressed Gases (Reinhold Publishing Corp., N.Y., 1985).

3. Gas Data Book (MATHESON Gas Products, East Rutherford, N.J., 1971), 6th ed.

4. Compressed Gases, Safe Practices Pamphlet No. 95, National Safety Council, Chicago, IL.

5. Pressure Relief Device Standards, Part I, Cylinders for Compressed Gases, Pamphlet S-1.1,Compressed Gas Association, Inc., Arlington, VA.

6. COWARD, H.F. and JONES, G.W., Limits of Flammability of Gases and Vapors, Bulletin 503,Bureau of Mines, Government Printing Office, Washington, D.C.

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