L2 - Occupational Health Hazards.pptx

OCCUPATIONAL SAFETY & HEALTH
OCCUPATIONAL HEALTH HAZARDS
NOISE & VIBRATION
COLD & HEAT STRESS
ASSISTANT PROFESSOR PRACHI DESSAI, DON BOSCO COLLEGE OF ENGINEERING
D. L. GOETSCH; OCCUPATIONAL SAFETY AND HEALTH FOR TECHNOLOGISTS; ENGINEERS AND
MANAGERS
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TERMS
 Sound
 propagation, transmission and reception of waves in some medium, most commonly air.
 Decibel (dB)
 The unit used to express the intensity of sound.
 Threshold of discomfort is between 85 and 95 dB
 Threshold of pain is between 120 and 140 dB.
 Dosimeter
 The instrument that measures sound levels over a specified interval, stores the measures, and calculates the
sound as a function of sound level and sound duration.
 Noise. Any unwanted sound.
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TERMS
 Noise dose
 Noise exposure expressed as a percentage of the allowable daily exposure.
 100 percent dose equals an eight-hour exposure to a continuous 90-dBA noise
 Hazardous noise
 Sound for which any combination of frequency, intensity, or duration is capable of causing permanent hearing
loss in a specified population.
 Hertz (Hz). The unit measurement for audio frequencies.
 The frequency range for human hearing lies between 20 Hz and approximately 20,000 Hz.
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HAZARD LEVELS AND RISKS
 The most important of these are
 Intensity of the noise (sound pressure level)
 Type of noise (wide band, narrow band, or impulse)
 Duration of daily exposure
 Total duration of exposure (number of years)
 Age of the individual
 Coexisting hearing disease
 Nature of environment in which exposure occurs
 Distance of the individual from the source of the noise
 Position of the ears relative to the sound waves
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HAZARD LEVELS AND RISKS
 The most critical are the sound level, frequency, duration, and distribution of noise
 The unprotected human ear is at risk when exposed to sound levels exceeding 115 dBA.
 Exposure to sound levels below 80 dBA is generally considered safe.
 To decrease the risk of hearing loss, exposure to noise should be limited to a maximum eight-hour TWA
of 85 dBA.
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STANDARDS AND REGULATIONS
Primary sources of standards
and regulations relating to
noise hazards
OSHA
The American National
Standards Institute (ANSI)
NIOSH (The National Institute
for Occupational Safety and
Health)
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ANSI STANDARD
 The two procedures identified were as follows:
Percent worse sequential
 This procedure identifies the percentage of subjects who show a deterioration of 15 dBA or more in their
ability to hear at least one test frequency in either ear between two sequential audiograms.
Percent better or worse sequential.
 This procedure identifies the percentage of subjects who show either a deterioration or an improvement of 15
dBA or more in thresholds for at least one test frequency in either ear between two sequential audiograms.
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ANSI STANDARD
Results of tests are compared in sequence
 The results of year 4 are compared with those of year 3.
 The results of year 3 are compared with those of year 2, and so on.
 In this way, a current audiogram is compared against an earlier audiogram.
 The results of the earlier test are used as a baseline for comparison.
Test results from several employees in a given work unit are examined individually and compared with past
results sequentially.
If enough employees show hearing loss, the conclusion may be that the work unit’s hearing conservation
program is ineffective.
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OSHA REGULATIONS
The basic requirements generated from this standard for hearing conservation programs are as follows:
 Hearing hazards monitoring
 Engineering and administrative controls
 Audiometric evaluation
 Personal hearing-protection devices
 Education and motivation
 Record keeping
 Program evaluation
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HEARING HAZARDS MONITORING
 Hearing hazard exposure monitoring is conducted for various purposes, including
 Determining whether hazards to hearing exist
 Determining whether noise presents a safety hazard by interfering with speech communication or
the recognition of audible warning signals
 Identifying employees for inclusion in the hearing loss prevention program
 Classifying employees’ noise exposures for prioritizing noise control efforts and defining and
establishing hearing protection practices • Evaluating specific noise sources for noise control
purposes
 Evaluating the success of noise control efforts various kinds of incrementation and measurement
methods may be used, depending on the type of measurements being conducted
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ENGINEERING AND ADMINISTRATIVE
CONTROLS
 Engineering and administrative controls represent the first two echelons in the hierarchy of controls:
 remove the hazard
 remove the worker.
 Typical engineering controls involve:
 Reducing noise at the source (for example, installing a muffler)
 Interrupting the noise path (for example, erecting acoustical enclosures and barriers)
 Reducing reverberation (for example, installing sound-absorbing material)
 Reducing structure-borne vibration (for example, installing vibration mounts and providing proper
lubrication)
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ENGINEERING AND ADMINISTRATIVE
CONTROLS
 Administrative controls - changes in the work schedule or operations that reduce noise exposure, may
also be used effectively.
 Operating a noisy machine on the second or third shift when fewer people are exposed
 Shifting an employee to a less noisy job once a hazardous daily noise dose has been reached.
 Practice of rotating employees between quiet and noisy jobs
 Provide for quiet areas where employees can gain relief from workplace noise.
 Areas used for work breaks and lunchrooms should be located away from noise.
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AUDIOMETRIC EVALUATION
 For maximum protection of employees, audiograms should be performed on the following occasions:
 Preemployment
 Prior to initial assignment in a hearing hazardous work area
 Annually as long as the employee is assigned to a noisy job (a TWA exposure level equal to or
greater than 85 dBA)
 At the time of reassignment out of a hearing hazardous job
 At the termination of employment
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PERSONAL HEARING PROTECTION DEVICES
 Passive earmuffs - They consist of ear cups lined with foam and block noise using nothing but the
foam-lined cups. The primary weakness of passive earmuffs is they tend to block out not just
unwanted noise, but also certain advantageous sounds such as voices trying to warn of danger.
 Uniform attenuation earmuffs - These earmuffs not only block noise, but also attenuate the noise more
uniformly within several key octave bands (250 Hz to 4 KHz). This allows employees wearing them
to hear certain important sounds such as spoken instructions or warnings, thus reducing one of the
main safety risks associated with earmuffs.
 Electronic earmuffs -This type of earmuff uses electronic technology to both block and modulate
sound. Some of the more popular brands of electronic earmuffs can receive AM/FM radio signals or
have a wireless connection to a CD or MP3 player.
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EDUCATION AND MOTIVATION
 Training is a critical element of a good hearing loss prevention program.
 In order to obtain sincere and energetic support by the management and active participation by
employees, it is necessary to educate and motivate both groups.
 A hearing loss prevention program that overlooks the importance of education and motivation is likely
to fail because employees will not understand why it is in their best interest to cooperate, and
management will fail to make the necessary commitment.
 Employees and managers who appreciate the precious sense of hearing and understand the reasons for,
and the mechanics of, the hearing loss prevention program will be more likely to participate for their
mutual benefit, rather than viewing the program as an imposition.
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RECORD KEEPING
 Audiometric comparisons, reports of hearing protector use, and the analysis of hazardous exposure
measurements all involve the keeping of records.
 Unfortunately, records are often kept poorly because there is no organized system in place, and in many
cases, those responsible for maintaining the records do not understand their value.
 OSHA’s latest version of the Form 300 Log has a column for recording hearing loss.
 Many companies have found that their record-keeping system is inadequate only when they discover that
they need accurate information. This sometimes occurs during the processing of compensation claims.
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PROGRAM EVALUATION
 The primary goal of any hearing loss prevention program must be to reduce, and eventually eliminate,
hearing loss due to workplace exposures.
 Although management may have the best intentions of implementing this goal and a company’s
hearing loss prevention program may have the appearance of being complete and complying with
OSHA’s requirements, the program still may not achieve this goal.
 There are two basic approaches to following program evaluation: (1) assess the completeness and
quality of the program’s components and (2) evaluate the audiometric data.
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WORKERS’ COMPENSATION AND NOISE
HAZARDS
 Hearing loss claims are being covered by state workers’ compensation laws
 In making determinations of such relationships, physicians consider the following factors:
 Onset and progress of the employee’s history of hearing loss
 The employee’s complete work history
 Results of the employee’s otological examination
 Results of hearing studies that have been performed
 Determination of whether causes of hearing loss originated outside the workplace
 Because, approximately 15 percent of all working people are exposed to noise levels exceeding 90
dBA, hearing loss may be as significant in workers’ compensation costs in the future as back injuries,
carpal tunnel syndrome, and stress are now significant
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NOISE CONTROL STRATEGIES
 Noise can be reduced at its source
 Enclosing the source
 Altering the acoustical design at the source
 Substituting equipment that produces less noise
 Making alterations to existing equipment,
 Changing the process so that less noisy equipment can be used.
 Noise can be reduced at the receiver by enclosing the worker, using personal protective devices, and
changing job schedules so that exposure time is reduced.
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HEARING PROTECTION DEVICES
 Enclosures are devices that completely encompass the employee’s head, much like the helmets worn
by motorcycle riders.
 Earplugs (also known as aurals) are devices that fit into the ear canal. Custom-molded earplugs are
designed and molded for the individual employee. Premolded earplugs are generic in nature, are
usually made of a soft rubber or plastic substance, and can be reused.
 Formable earplugs can be used by anyone. They are designed to be formed individually to a person’s
ears, used once, and then discarded.
 Superaural caps fit over the external edge of the ear canal and are held in place by a headband.
Earmuffs, also known as circumaurals, cover the entire ear with a cushioned cup that is attached to a
headband. Earplugs and earmuffs are able to reduce noise by 20 to 30 dB. By combining earplugs and
earmuffs, an additional 3 to 5 dB of blockage can be gained.
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MANAGERS
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COLD AND HEAT STRESS
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INTRODUCTION
 Deep body temperature - falling below 36°C (96.8°F)
 A fatal exposure to cold typically results from failure to remove the employee from a cold air
environment or immersion in cold water.
 Excessive exposure to cold stress, even when not fatal, can result in impaired judgment, reduced
alertness, and poor decision making.
 Acute cold stress can cause reduced muscular function, decreased tactile sensitivity, reduced
blood flow, and thickening of the synovial fluid.
 Chronic cold stress can lead to reduced functioning of the peripheral nervous system.
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INTRODUCTION
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For example, if employees are working in an environment that is 30°F and has a wind
speed of 15 miles per hour (mph), the equivalent temperature is 9°F.

PREVENTING COLD STRESS
 For example, employees working a four-hour
shift in an environment with an air temperature
of -34°C and a 5-mph wind TLVs for a Four-
Hour Shift should be exposed no longer than
55 minutes at a time and should warm up at
least three times during the shift.
MANAGERS
26

STRATEGIES THAT CAN BE USED TO DECREASE
THE HAZARDS OF COLD STRESS
 Reduce the effect of the wind by
 erecting a windscreen
 wearing wind-breaking clothing.
 When working in a setting in which clothing may get wet, apply one or more of the following strategies:
 with light work, wear an outer layer of impermeable clothing;
 with heavier work, wear an outer layer that is water-repellent, but not impermeable (change outerwear as it
becomes wet)
 select outer garments that are ventilated to prevent internal wetting from sweat;
 if clothing gets wet before going into the cold environment, change first
 change socks daily or more often to keep them dry
 use vapor barrier boots to help keep the feet dry
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 Additional strategies should be applied:
 Direct supervision or the buddy system.
 When heavy work is necessary, employees should take frequent warming breaks in heated shelters.
 If clothing becomes wet—internally or externally—it should be changed during a break.
 Do not allow new employees to work full time in these conditions until they have several days to become
accustomed to the conditions and the necessary protective clothing.
 When determining the required work level for employees (light, heavy, or very heavy), consider the weight
and bulkiness of protective clothing.
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 Additional strategies should be applied:
 Organize work in cold environments to minimize long periods of sitting or standing still. Never use
unprotected metal chairs or seats.
 Before allowing employees to work in a cold environment, make sure they have been trained in safety and
health procedures.
 When work in a refrigerated room is required, the air velocity should be minimized and maintained at one
meter per second (200 feet per minute) or less.
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 Outdoors in snow - employees should be provided special safety goggles that protect the eyes
from ultraviolet light, glare, and blowing ice crystals.
 Employees who suffer from diseases or take medications that inhibit normal body functions or
that reduce normal body tolerances should be prohibited from working in environments where
temperatures are at 21°C (69.8°F) or less.
 Employees who are routinely exposed to the following conditions should be medically certified
as being suitable for work in such conditions: (1) air temperatures of less than 24°C (11.2°F)
with wind speeds less than 5 mph; and (2) air temperatures of less than 18°C (0.4°F) with wind
speeds greater than 5 mp
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HEAT STRESS
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IMPORTANT TERMS
 Heat stress: is the net heat load to which a worker may be exposed from the combined contributions of
metabolic effect of work, environmental factors (i.e., air temperature, humidity, air movement, and
radiant heat exchange), and clothing requirements.
 Heat Strain: is the overall physiological response resulting from heat stress. The physiological
adjustments are dedicated to dissipating excess heat from the body. Acclimatization is a gradual
physiological adaptation that improves an individual’s ability to tolerate heat stress.
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IMPORTANT TERMS
 Heat exhaustion. This is a physical state in which the worker’s skin becomes clammy and moist and
his or her body temperature is still normal or slightly higher than normal.
 Heat exhaustion results from loss through sweating off fluid and salt that are not properly replaced
during exertion.
 Heatstroke. This is a physical state in which the worker’s skin becomes hot and dry, there is mental
confusion, and there may be seizures or convulsions.
 Heat cramps. Heat cramps are muscle cramps that can occur when workers exert themselves
sufficiently to lose fluids and salt through sweating, but replace only the fluids by drinking large
amounts of water containing no salt
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RECOGNIZING HEAT STRAIN
 Exposure to heat stress should be stopped immediately for any employee experiencing any of these
symptoms:
 A sustained rapid heart rate (180 beats per minutes minus the employee’s age in years). For
example, a 40-year-old employee has a sustained heart rate of 150 beats per minutes. This is a
problem because the heart rate exceeds 140 (180 minus 40) beats per minute.
 Core body temperature is greater than 38.5°C.
 Recovery rate minute after a peak work effort is greater than 110 beats per minute.
 Sudden and severe fatigue, nausea, dizziness, or light-headedness.
 Profuse sweating that continues for hours.
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 Several acclimatized employees have a job to do that has a work demand of 75 percent work and 25 percent
rest. The WBGT has been computed as 26. The work is considered “heavy.” Because the employees will wear
long-sleeved shirts and long trousers made of woven material an additional 3.5° must be added: 26 3.5
29.5°C. Using the proper column and row of Figure 16–1, a WBGT of 26 can be determined. Because the
calculated and adjusted WBGT is 29.5, there is a problem. In order to work in these conditions, the employees
should adjust the work demand to 25 percent work and 75 percent rest.

HEAT STRESS MANAGEMENT SAFETY
 Provide accurate verbal and written instructions, training programs, and other information about heat
stress and strain.
 Encourage drinking small volumes (approximately one cup) of cool water about every 20 minutes.
 Encourage coworker observation to detect signs and symptoms of heat strain in others.
 Counsel and monitor those employees who take medications that may compromise normal
cardiovascular, blood pressure, body temperature regulation, renal, or sweat gland functions, and those
who abuse or who are recovering from the abuse of alcohol and other intoxicants.
 Encourage healthy lifestyles, ideal body weight, and electrolyte balance.
 Adjust expectations of those returning to work after absence from heat stress situations and encourage
consumption of salty foods (with approval of the employee’s physician if on a salt-restricted diet).
 Consider replacement medical screening to identify those susceptible to systemic heat injury.
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SPECIFIC CONTROLS FOP HEAT STRESS
MANAGEMENT
 The ACGIH recommends the following specific controls:
 Establish engineering controls that reduce the metabolic rate, provide general air movement,
reduce process heat and water-vapor release, and shield radiant heat sources, among others.
 Consider administrative controls that set acceptable exposure times, allow sufficient recovery, and
limit physiological strain.
 Consider personal protection that has been demonstrated to be effective for the specific work
practices and conditions at the location.5
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IMPROPER ILLUMINATION
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WHAT ARE SOME OF THE MOST COMMON
LIGHTING PROBLEMS?
Poor lighting can cause several problems
such as:
 Insufficient light – not enough (too little)
light for the need.
 Glare – too much light for the need.
 Improper contrast.
 Poorly distributed light.
 Flicker.
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WHAT SHOULD YOU KNOW ABOUT INSUFFICIENT
LIGHT?
The amount of light we need varies and
depends on:
 Type of task being done (such as
demands for speed and accuracy).
 Type of surfaces (does it reflect or
absorb light).
 General work area.
 Individual's vision.
 The amount of light falling on a
surface is measured in units called
lux. Depending on the factors noted
above, adequate general lighting is
usually between 500 and 1000 lux
when measured 76 cm (30 inches)
above the floor.*
Recommended Illumination Levels*
Type of Activity Ranges of Illuminations (Lux)**
Public spaces with dark surroundings 20-50
Simple orientation for short temporary
visits
50-100
Working spaces where visual tasks are only
occasionally performed
100-200
Performance of visual tasks of high
contrast or large scale
200-500
Performance of visual tasks of medium
contrast or small size
500-1000
Performance of visual tasks of low contrast
or very small size
1000-2000
Performance of visual tasks of low contrast
and very small size over a prolonged
period
2000-5000
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EFFECTS OF POOR LIGHTING AT WORKPLACE
Eye strain due to Poor Lighting
 Poor lighting usually leaves the person with eye strain. Eye strain is a very uncomfortable feeling. It
can also get linked up with other eye related problems. If one spends more time working in poor
lighting, the quality of his vision may start to deteriorate. Also most of the workplaces involve
working with computers. This with poor lighting will definitely result in eye strain and eventually
deteriorate eye vision.
 To avoid eye strain due to poor lighting, one can set the contrast and brightness of the computer screen
to his comfort level and make use of desk lamps to ensure proper lighting. If possible one can also
shift his table near the window to receive natural light on his work table.
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Headache
 This one of the common effect of Poor lighting at workplace. Working with poor lighting might leave
one with headaches, as one has a trouble focusing on the computer screen or on the work in front of
them. Headaches will prevent you from being effective at work, thus reducing your efficiency.
 To avoid headaches due to poor lighting, one can also make use of desk lamps or computer lamp to
bright up the work table area, but before doing so the reasons for poor lighting must be checked and
accordingly actions should be taken.
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Posture
 Painful back and neck are a result of poor lighting. Poor lighting usually makes you sit in an
uncomfortable position while working. The pain in the back and neck can fade away with the use of
stretching and yoga, but ensuring proper lighting systems will help you eliminate the cause.
Accidents
 This is very dangerous effect of Poor Lighting at Workplace among all. In poor light it becomes
difficult to estimate shape, size or depth of space or objects. It thus becomes a place where accidents
of any type can occur. Due to this, many a times it is said “Poor lighting is safety and health hazard”.
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HOW MUCH LIGHT IS NEEDED FOR VARIOUS
SITUATIONS OR ACTIVITIES?
To reach proper light levels and uniform light distribution in the
visual environment, many light fixtures are designed to reflect
light off walls, ceilings and objects. The amount of light reflected
off a surface can be measured. Suggestions for the percent of light
reflected off surfaces in a typical office include:
 Window blinds (40-50%).
 Walls (50% maximum).
 Business machines (50% maximum).
 Ceiling (70-80%).
 Floor (20-40%).
 Furniture (25-45%).
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HOW TO AVOID EFFECTS OF POOR LIGHTING AT
WORKPLACE?
Add more lamps for Poor Lighting Solution
 To increase light intensity in office or home we can increase the number of lamps / bulbs to tackle
poor lighting. We can use LED bulbs to control electricity bills.
Reduce Lighting in case of Glares
 Identify the source of Glare and change the position of it. If it is due to light source the change the
position or place of the power source. If it is because of anything shiny then we can coat with matte or
change the angle of the reflector. We can also use Glare reduction Glass to reduce glares.
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HOW TO AVOID EFFECTS OF POOR LIGHTING AT
WORKPLACE?
Change the Color of the Room for Poor Lighting
 Paint your home or office with light colour so that you can get maximum reflection of existing light.
Lighter shades also make you feel the room bigger.
Make Windows Bigger
 If you have small windows then make them bigger. This will not only save your electricity bills but
also improve the airflow or air circulation in your home or office.
Rearrange the desks
 In case of wrong place where extra lighting is not possible you can move to a place in your office or
home where light is brighter. Please do not place light source just behind the worker.
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HOW DO YOU TEST AND CORRECT FOR
INSUFFICIENT LIGHT PROBLEMS?
To detect insufficient light, try the following:
 Measure the average illumination throughout
the workplace. Compare this to the
recommended levels.
 Look for shadows, especially over work areas
and on stairways.
 Ask workers if they suffer from eye strain or
squint to see, or get frequent headaches.
 Workers should sit in their normal working
positions during measurement to give you
accurate results.
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HOW DO YOU TEST AND CORRECT FOR
INSUFFICIENT LIGHT PROBLEMS?
To correct insufficient light:
 Replace bulbs on a regular schedule. Old bulbs give less light than new ones, so replace them
before they burn out. Follow manufacturers' instructions.
 Clean light fixtures regularly. Dirt on light fixtures reduces the amount of light given off. Light
fixtures with open tops allow air currents to move dust up through the fixtures so dust and dirt do
not accumulate on them.
 Add more light fixtures in appropriate places.
 Paint walls and ceilings light colors so light can be reflected.
 Use more reflected light and local lighting to eliminate shadows. For example, a covered light
mounted under a transparent guard on a grinding wheel provides the added light needed to
clearly see the task.
 Do not position the work station with the light fixture directly behind worker.
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WHAT SHOULD YOU KNOW ABOUT GLARE?
Glare is a common lighting problem.
Glare is what happens when a bright light source or reflection interferes with how you are 'seeing' an
object
Reflected glare is caused by:
 Light reflected from polished, shiny or glossy surfaces.
 Glass on picture frames, or windows at night.
 Monitors / screens.
 Direct glare is caused by:
 Very bright light from poorly positioned light fixtures.
 Sunlight.
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HOW DO YOU DETECT GLARE?
 When in your normal working position, look at a
distant object at eye level. Block the light "path" from
the fixtures with a book or cardboard. If the distant
object is now easier to see, the light fixtures are
probably producing glare.
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HOW DO YOU DETECT GLARE?
 To detect reflected glare, look at the task
from your normal working position.
Block the light falling on it from the
front or above. If details are now easier
to see, reflections are a problem.
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HOW DO YOU CORRECT GLARE PROBLEMS?
To correct glare, try:
 Using several small low-intensity light
fixtures rather than one large high-intensity
light fixture.
 Using light fixtures that diffuse or
concentrate light well. Indirect light fixtures
or direct light fixtures with parabolic louvres
are two possibilities.
 Covering bare bulbs with louvers, lenses or
other devices to control light.
 Increasing the brightness of the area around
the glare source.
 Using adjustable local lighting with
brightness controls.
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HOW DO YOU CORRECT GLARE PROBLEMS?
 Positioning light fixtures to reduce reflected
light that is directed toward the eyes.
 Using low gloss paper or applying flat or
semi-gloss paint and matte finishes on
'offending' surfaces. Removing highly
polished and shiny objects.
 Keeping general lighting levels at
recommended levels.
 Positioning the work station so that windows
and fluorescent light tubes are parallel to the
worker's line of sight.
 Position the work station so that the light
fixtures are NOT in the front or directly
overhead.
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PERMISSIBLE EXPOSURE LIMITS
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WHAT ARE THE OCCUPATIONAL EXPOSURE
LIMITS?
 Occupational exposure limit (OEL) - represents the maximum airborne concentration of a toxic
substance to which a worker can be exposed over a period of time without suffering any harmful
consequences.
 These limits are set out by:
 American Conference of Governmental Industrial Hygienists (ACGIH)
 National Institute for Occupational Safety and Health (NIOSH) in the United States.
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ARE THERE DIFFERENT TYPES OF EXPOSURE
LIMITS?
 ACGIH defines three categories of threshold limit values:
 Threshold Limit Value – Time-Weighted Average (TLV-TWA): The concentration of a hazardous
substance in the air averaged over an 8-hour workday and a 40-hour workweek to which it is
believed that workers may be repeatedly exposed, day after day, for a working lifetime without
adverse effects.
 Threshold Limit Value – Short-term exposure (TLV-STEL): A 15-minute time weighted average
exposure that should not be exceeded at any time during a workday, even if the overall 8-hour
TLV-TWA is below the TLV-TWA.
 Workers should not be exposed more than four times per day to concentrations between TLV-
TWA and TLV-STEL.
 There should be at least a 60 minute interval between exposures. The short-term exposure
threshold has been adopted to account for the acute effects of substances that have primarily
chronic affects.
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LIMITS?
 Threshold Limit Value – Ceiling (TLV-C): This is the concentration that should not be exceeded
during any part of the working exposure. Peak exposures should be always controlled. For substances
that do not have TLV-TWA or TLV-C established, the maximum admissible peak concentrations must
not exceed:
 Three-times the value of the TLV-TWA for no more than 15 minutes, no more than four times per
workday. Exposures must be at least 1 hour apart during the workday.
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LIMITS?
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L2 - Occupational Health Hazards.pptx