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Occupational Health Courses

Dr. Ahmed-Refat

Professor of Occupational Medicine

Tibah University, KSA, March ,2012

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1- Assessment

of Work Place Hazards:

Measuring Tools and Principles

Introduction:

Occupational Hygiene:

"The discipline of anticipating, recognizing,

evaluating and controlling health hazards in the

working environment with the objective of

protecting worker health and well-being and

safeguarding the community at large.

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Components of Occupational Hygiene:

—

— ANTICIPATION – this involves identifying

potential hazards in the workplace before

they are introduced.

—

— RECOGNITION - this involves identifying the

potential hazard.

—

— EVALUATION of the extent of exposure to

hazards in the workplace. This often involves

measurement of the personal exposure of a

worker to the hazard in the workplace, and

— assessment of the data in terms of

recommended occupational exposure limits

(OELs), where such criteria exist.

Controlling health hazards in the working

environment.

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I- Measuring of

Physical Hazards

A- Noise

Basic Concepts :

Sound is fluctuations in pressure above and below the

ambient pressure of a medium that has elasticity and

viscosity. The medium may be a solid, liquid, or gas.

Sound is the auditory sensation evoked by the oscillations

in pressure .

Noise = unwanted sound,

Sound perceived by the ear results from

fluctuations

( Frequency – cycle per second - Hz )

the pressure

( Intensity- Power – Loudness –Energy – dB )

of the air.

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Decibel: The decibel ( dB) is a dimensionless quantity.

Unit of Sound/ Noise intensity

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dB weighting:

• A-weighting’, or dB(A), is used to measure

average noise levels as it approximates the

sensitivity of the human ear at low noise

levels. This is typically used to assess for the

potential of hearing loss

‘C-weighting’, or dB(C), is used to measure

peak, impact or explosive noises. This

weighting is used to determine suitable

personal hearing protection equipment in

high noise environments

3dB change in noise level results in a doubling of the noise

Workplace Noise Levels

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B- Light

Basic Concepts:

Measuring of Workplace

Illumination

Light meter / 'Lux' meter).

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What is a light meter?

A light meter measures the level (amount) of visible light (illumination) in a given area tested.

Illumination is expressed in units of lumens per square meter LUX (metric) and

lumens per square ft. Foot candles/ Fc (English).

Convert Foot candles, LUX, and Lumens:

• Multiply Foot candles by 10.76891 to convert to LUX

• Multiply LUX by 0.09290304 to convert to Foot candles

• Foot candles = Lumens per sq. ft.

Sun = 107,527 Lux

Full day light = 10,752 Lux

Full moon = 108 Lux

Work place Adequate Light ( office ):

• General background 160–240 Lux

• Routine office work (typing, filing) 400 Lux

• Work with poor contrast (proof reading) 600 Lux.

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Minimum Illumination Intensity on

Objects of Work

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C- Heat

Basic Concepts:

HEAT STRESS

“The net heat load to which a worker may be exposed from the

combined contributions of metabolic cost of work, environmental

factors (ie air temperature, humidity, air movement and radiant heat

exchange) and clothing requirements.”

HEAT STRAIN

“The physiological impact of heat stress on the body, as

expressed in terms of changes in tissue temperatures and

compensatory changes in the activity of physiological systems

(sweat rate, heart rate, skin blood flow).”

Heat strain =

“The overall physiological response resulting from heat stress.”

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Temperature Levels and its effects

46.5°C Highest recorded survivable core temperature

43°C Tissue damage (brain, liver)

41°C Cessation of sweating

39°C The threshold of hyperthermia

36.8°C Normal core temperature

35°C The threshold of hypothermia

33°C Impaired muscle function, introversion, loss of mental

alertness

30°C Cessation of shivering and then unconsciousness

28°C Possible ventricular fibrillation

26°C Bradycardia and bradypnoea

24°C Possible death without rewarming

14.4°C Lowest recorded core temperature for a survivor of accidental

hypothermia

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Damaging Effects of Heat Exposure

>50°C Second-degree burn

>45°C Tissue damage

41 – 43°C Burning pain

39 – 41°C Pain

33 – 39°C Skin warmth through to discomfort (hot)

28 – 33°C Thermal comfort

25 – 28°C Cool through to discomfort (cold)

15°C Pain

10°C Loss of skin sensation

5°C Non-freezing cold injury: (time dependent, and can occur

between 17 – 0.55°C)

<0.55°C Freezing cold injury (frostbite)

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Measuring of Thermal Environment

Measurement of air temperature is usually made

with one of the following techniques:

Mercury-in-glass thermometer

Thermocouple

Platinum resistance thermometer

Thermistor

A- Mean Radiant Temperature

Measurement of the mean radiant

temperature can be derived from

the readings of a black globe

thermometer. This consists of

a hollow black globe usually made

of copper (due to its high

conductivity) in the centre of

which is placed a temperature

sensor .

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B- Humidity

• Air contains a certain amount of water vapour • Higher air temperature

– more water vapour can be contained in the air • Lower air temperature

– less water vapour can be contained in the air

The absolute humidity is defined as the mass of water vapour in air

per unit volume of air/water vapour mixture and has units of kg m-3.

Relative humidity is defined as:

“The ratio of the prevailing partial pressure of water vapour to the

saturated water vapour pressure.”

The “dew point” is the temperature at which the air becomes

saturated.

Dry & wet Bulb Thermometer

• Water evaporating from a surface reduces the temperature of

the surface

• If the bulb of a thermometer is covered by a damp fabric

sleeve water evaporating causes a lower reading - this is

termed the wet bulb temperature

• The difference between dry bulb temperature and wet bulb

temperature can be used to determine relative humidity

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• At 100% relative humidity no evaporation takes place so the

dry bulb temperature and wet bulb temperature will be the

same

Measuring relative Humidity

• One of the most commonly used instruments for determining

humidity is the whirling hygrometer, which is also called a

sling psychrometer (Figure 5.2).

Whirling hygrometer

one dry bulb thermometer

one wet bulb thermometer - bulb covered with wick

dipped into distilled water reservoir

air flow (> 4 metres / sec) achieved by ‘whirling’

read wet bulb temperature first, then dry bulb

Its operation is relatively simple. The sling psychrometer consists of two thermometers, a wet bulb and dry bulb. A “wick” or “sock” covers one of

the thermometers (the “wet” bulb) and should be thoroughly wetted using distilled (de-ionised) water prior to taking any measurements. This involves filling the water reservoir at the end of the psychrometer and may

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also involve manually wetting the wick. Care should be taken not to

contaminate the wick with dirty fingers or water that is not de-ionised. The handle is then unclipped and the psychrometer is swung for at least

20 – 30 seconds. This will allow an air movement to pass over the wet

bulb thermometer and initiate evaporation of water from the wick. After

20 – 30 seconds, the aspirated wet bulb temperature is read first (then

the dry bulb temperature). These values are noted and the

measurements repeated three times. Optimally, the repeated

measurements should be within ±1°C of

Calculation

Psychrometric charts

– Charts that inter-relate – vapour pressure (water content) – relative humidity – dry bulb temperature – wet bulb temperature

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Measurement of Air Velocity

Air movement across the body can influence heat flow to and from the body

and hence body temperature

Air velocity can be measured by a number of methods

• Vane anemometer

– Directional & not accurate at low velocities

• Hot-wire anemometer

– Directional & inaccurate at low velocities

• Kata thermometer

– Omni-directional but not suited to conditions where large or

rapid variations in air movement occur

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Vane anemometer

Hot-wire Anemometer

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Kata Thermometer

• Principle of operation

– thermometer with large bulb

– two marks on stem (3K apart)

– heated so that fluid is above higher mark

– fixed in monitoring position

– allowed to cool

– time for fluid to cool to lower mark noted

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Wet Bulb Globe Thermometer

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Wet Bulb Globe Thermometer

Calculation of WBGT

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II- Chemical Hazards Physical States of chemicals

•

• Vapour - the gaseous state of a substance which is liquid at

25°C and 760 mm Hg (STP).

• Mist - liquid particles, large size generally produced by

bubbling, splashing or boiling of a liquid.

• Fume - Solid particles produced by condensation from a liquid

or a reaction between two gases. The particle size of a fume

<1 micron (µm) diameter anything larger is considered a dust

particle.

•

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• Dust - particles of solid material in the broad size range of 1

micron to 1 millimetre diameter. Anything of a larger particle

size is considered to be grit and will be too heavy to remain

airborne.

• Aerosol - general term for the dispersions of solid or liquid

particles of microscopic size in a gaseous medium e.g. fog,

smoke etc. although commonly used to term fine liquid spray

(e.g. ‘aerosol can’).

Fibre – Solid particulate which are long and thin i.e. have a high

aspect ratio of length to breadth.

Types of Sampling

• Grab

• Short term

• Long term

• Continuous

Sampling Pattern

• Grab sampling

• Task duration sampling

• Short period sampling (less than the task duration and sometimes taken consecutively)

• Full shift sampling

•

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Grab

Short Term

Co

nce

ntr

atio

n

Time

Co

nce

ntr

atio

n

Time

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Long Term

Continuous

Co

nce

ntr

atio

n

Time

Co

nce

ntr

atio

n

Time

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Sampling for Particulates/Dust

Particle Size Distribution

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Particle size

Total inhalable dust is the fraction of airborne

material which enters the nose and mouth during

breathing and is therefore liable to deposition

anywhere in the respiratory tract. The particle sizes

of total inhalable dust are up to 100 microns.

Respirable dust is that fraction that penetrates to the

deep lung where gas exchange takes place. The

particle sizes of respirable dust are up to 10 microns

Breathing Zone

As the main route of entry into the body for many substances is

via inhalation, it is logical that any estimate of exposure of such

substances should be conducted in a location consistent with

normal inhalation patterns of workers. By convention, this has

been deemed the “breathing zone” .

“A hemisphere of 300 mm radius extending in front of the face and

measured from the midpoint of a line joining the ears.”

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Elements of a Sampling System

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Sampling for Gases and Vapours

• Active Sampling - i.e. by means of a

mechanic/sampling pump method.

– Sorbent Tubes

• Passive Sampling

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Indicator Tubes (Gas Grab Sampling)

Before ( Left) and after sampling (Right)

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HYGIENE STANDARDS

By “hygiene standard” we are referring to the level of

exposure, via inhalation, that should not cause ill health to

a healthy adult when exposed to a contaminant. The

results from air sampling can thus be compared against

these standards and can be used as a guide to assist in

the control of health hazards. Other names for hygiene

standards commonly used throughout the world are

Threshold Limit Values (TLVs®), Exposure Standards (ES),

Occupational Exposure Limits (OEL), Workplace Exposure

Limits (WEL). In general all such terminology is

interchangeable.

The best known list of “hygiene standards” is the

Threshold Limit Values (TLVs®) produced by the American

Conference of Governmental Industrial Hygienists

Threshold Limit Values (TLVs®) refer to airborne concentrations of

chemical substances and represent conditions under which it is

believed that nearly all workers may be repeatedly exposed, day

after day, over a working lifetime, without adverse health effects.

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There are three types of TLVs® 1. TLV-Time Weighted Average (TLV-TWA)

2. TLV-Short Term Exposure Limit (TLV-STEL)

3. TLV-Ceiling (TLV-C)

4.3.1 TLV-TWA “The TWA concentration for a conventional 8-hour

workday and a 40-hour work week, to which it is believed that nearly all workers may be repeatedly exposed, day after day, for a working lifetime without adverse effect.”

TLV-STEL “A 15 minute TWA exposure that should not be exceeded at

any time during a workday, even if the TWA is within TLV-TWA. The TLV-STEL is the concentration to which it is believed that

workers can be exposed continuously for a short period without suffering from:

1. irritation 2. chronic or irreversible tissue damage 3. dose-rate dependent toxic effects, or 4. narcosis of sufficient degree to increase the likelihood of accidental injury, impaired self rescue, or materially reduced work efficiency.”

TLV-C “The concentration that should not be exceeded during

any part of the working exposure.

If instantaneous measurements are not available, sampling should

be conducted for the minimum period of time sufficient to detect

exposures at or above the ceiling value.”

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Mixtures

When two or more hazardous substances have a similar

toxicological effect on the same target organ or system, their

combined effect rather than that of either individually, should be

given primary consideration.

In the absence of information to the contrary, different

substances should be considered as additive where the health

effect and target organ or systems is the same ie:

C1/TLV1 + C2/TLV2 + …… + Cn/TLVn ≤ 1

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Conversion of PPM to mg/m3