This document provides an overview of occupational health training courses focusing on assessment of workplace hazards. It discusses measuring physical hazards like noise, light, heat and thermal environment. Noise is measured using a sound level meter in decibels while light is measured in lux units using a lux meter. Heat stress and strain are also explained. Methods for measuring chemicals hazards like vapors, fumes and dust are outlined. Sampling techniques including grab, short term and long term sampling are covered. Hygiene standards used to evaluate exposure levels like TLVs are also mentioned.

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Occupational Health Courses
Dr. Ahmed-Refat
Professor of Occupational Medicine
Tibah University, KSA, March ,2012
www.SlideShare.net/AhmedRefat
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
Concentration
Time
Short Term
Concentration
Time
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Long Term
Concentration
Time
Continuous
Concentration
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
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