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Course 750 - Introduction to Industrial Hygiene

Safety guides and audits to make your job as a safety professional easier

Physical Hazards


Physical hazards that employees in the workplace face include excessive levels of ionizing and nonionizing electromagnetic radiation, noise, vibration, illumination, and temperature.

In occupations where there is exposure to ionizing radiation, time, distance, and shielding are important tools in ensuring worker safety. Danger from radiation increases with the amount of time one is exposed to it; hence, the shorter the time of exposure the smaller the radiation danger.

Distance also is a valuable tool in controlling exposure to both ionizing and non-ionizing radiation. Radiation levels from some sources can be estimated by comparing the squares of the distances between the worker and the source. For example, at a reference point of 10 feet from a source, the radiation is 1/100 of the intensity at 1 foot from the source.

Shielding also is a way to protect against radiation. The greater the protective mass between a radioactive source and the worker, the lower the radiation exposure.

Nonionizing radiation also is dealt with by shielding workers from the source. Sometimes limiting exposure times to nonionizing radiation or increasing the distance is not effective. Laser radiation, for example, cannot be controlled effectively by imposing time limits. An exposure can be hazardous that is faster than the blinking of an eye. Increasing the distance from a laser source may require miles before the energy level reaches a point where the exposure would not be harmful.

Noise, another significant physical hazard, can be controlled by various measures. Noise can be reduced by installing equipment and systems that have been engineered, designed, and built to operate quietly; by enclosing or shielding noisy equipment; by making certain that equipment is in good repair and properly maintained with all worn or unbalanced parts replaced; by mounting noisy equipment on special mounts to reduce vibration; and by installing silencers, mufflers, or baffles.

Substituting quiet work methods for noisy ones is another significant way to reduce noise, for example, welding parts rather than riveting them. Also, treating floors, ceilings, and walls with acoustical material can reduce reflected or reverberant noise. In addition, erecting sound barriers at adjacent work stations around noisy operations will reduce worker exposure to noise generated at adjacent work stations.

It is also possible to reduce noise exposure by increasing the distance between the source and the receiver, by isolating workers in acoustical booths, limiting workers' exposure time to noise, and by providing hearing protection. OSHA requires that workers in noisy surroundings be periodically tested as a precaution against hearing loss.

Another physical hazard, radiant heat exposure in factories such as steel mills, can be controlled by installing reflective shields and by providing protective clothing.

1. Time, distance, and shielding are important tools in ensuring worker safety in occupations where there is exposure to _____,

a. non-ionizing radiation
b. noise
c. ionizing radiation
d. temperature extremes

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Ionizing & Non-Ionizing Radiation

The electromagnetic spectrum.
(Click to enlarge)

Radiation having a wide range of energies form the electromagnetic spectrum, which is illustrated to the right. The spectrum has two major divisions: non-ionizing radiation and ionizing radiation

Non-ionizing Radiation

Non-ionizing radiation does not have enough energy to dislodge electron charges from atoms. It ranges from extremely low frequency radiation, shown on the far left through the audible, microwave, and visible portions of the spectrum into the ultraviolet range.

Ionizing Radiation

Radiation beyond the ultraviolet range falls within the ionizing radiation range that has enough energy to remove tightly bounded electron charges from atoms, thus creating ions. We take advantage of its properties to generate electric power, to kill cancer cells, and in many manufacturing processes.

There are three main kinds of ionizing radiation:

  • Alpha particles, which include two protons and two neutrons
  • Beta particles, which are essentially electrons
  • Gamma and x-rays, which are pure energy (photons).

2. Which of the following is a type of non-ionizing radiation?

a. alpha particles
b. beta particles
c. gamma rays
d. microwaves

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Every year, millions of people in the United States are exposed to hazardous noise at work. Noise-related hearing loss has been listed as one of the most prevalent occupational health concerns in the United States for many years.

Exposure to high levels of noise can cause permanent hearing loss. Neither surgery nor a hearing aid can help correct this type of hearing loss. Short term exposure to loud noise can also cause a temporary change in hearing (your ears may feel stuffed up) or a ringing in your ears (tinnitus). These short-term problems may go away within a few minutes or hours after leaving the noisy area. However, repeated exposures to loud noise can lead to permanent tinnitus and/or hearing loss.

Loud noise can also create physical and psychological stress, reduce productivity, interfere with communication and concentration, and contribute to workplace accidents and injuries by making it difficult to hear warning signals. Noise-induced hearing loss limits your ability to hear high frequency sounds, understand speech, and seriously impairs your ability to communicate. The effects of hearing loss can be profound, as hearing loss can interfere with your ability to enjoy socializing with friends, playing with your children or grandchildren, or participating in other social activities you enjoy, and can lead to psychological and social isolation.

How Does the Ear Work?

Anatomy of the Inner Ear
(Click to enlarge)

When sound waves enter the outer ear, the vibrations impact the ear drum and are transmitted to the middle and inner ear. In the middle ear three small bones called the malleus (or hammer), the incus (or anvil), and the stapes (or stirrup) amplify and transmit the vibrations generated by the sound to the inner ear. The inner ear contains a snail-like structure called the cochlea which is filled with fluid and lined with cells with very fine hairs. These microscopic hairs move with the vibrations and convert the sound waves into nerve impulses - the result is the sound we hear.

Exposure to loud noise can destroy these hair cells and cause hearing loss!

Warning Signs of Noisy Workplace

Noise may be a problem in your workplace if:

  • You hear ringing or humming in your ears when you leave work.
  • You have to shout to be heard by a coworker an arm's length away.
  • You experience temporary hearing loss when leaving work.

3. Jack is leaving work and he hears ringing in his ears which is a sign he may be suffering from _____.

a. train the employee again
b. consider counseling after work
c. tinnitus
d. interview the employee's supervisor

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sound levels
Typical Sound Levels
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Noise (Continued)

Noise is measured in units of sound pressure levels called decibels, named after Alexander Graham Bell, using A-weighted sound levels (dBA). The A-weighted sound levels closely match the perception of loudness by the human ear. Decibels are measured on a logarithmic scale which means that a small change in the number of decibels results in a huge change in the amount of noise and the potential damage to a person's hearing.

Under OSHA standards, workers are not permitted to be exposed to an 8-hour TWA equal to or greater than 90 dBA. OSHA uses a 5-dBA exchange rate, meaning the noise level doubles with each additional 5 dBA. The following chart shows how long workers are permitted to be exposed to specific noise levels:

The values in the chart above are from Table G-16 in the general industry standard, 29 CFR 1910.95.

Permissible Duration
(Hours per Day)
Sound Level
(dBA, Slow Response)
16 85
8 90
4 95
2 100
1 105
½ 110
¼ or less 115

A worker's daily noise exposure typically comes from multiple sources, which have different noise levels for different durations. When adding different noise levels from various noise sources, only noise levels exceeding 80 dBA should be considered. The combined effect of these noise sources can be estimated using the following equation:

Sum = C1/T1 + C2/T2 + C3/T3 + Cn/Tn

Where Cn is the total duration of exposure at a specific noise level, and Tn is the total duration of noise permitted at that decibel level. If the sum equals or exceeds "1," the combined noise level is greater than the allowable level. If the sum is less than "1," the combined noise level is less than the allowable level.

Example: A worker in a machine shop is exposed to 95 dBA for 2 hours, 69 to 78 dBA for 4 hours (including a 15-minute break and 45-minute lunch), and 90 dBA for 3 additional hours.

Example: Worker's Activity Time Measured Sound Level
Milling machine 6:00 a.m. - 8:00 a.m. 95 dBA
Break room 8:00 a.m. - 8:15 a.m. 69 dBA
Parts department 8:15 a.m. - 11:15 a.m. 78 dBA
(in break room, 45 min.)
11:15 a.m. - 12:00 noon 69 dBA
Milling assist 12:00 noon - 3:00 p.m. 90 dBA

To determine if the worker's noise exposure exceeds a 90 dBA TWA, use the equation above. Because the noise levels in the break room (69 dBA) and parts department (78 dBA) are below 80 dBA, these periods of the day are not included in the calculation. According to the chart above, workers are permitted to be exposed to 95 dBA for 4 hours per day and 90 dBA for 8 hours per day. Calculate the ratio of actual exposure duration to permissible exposure duration for each time segment and add them: 2/4 + 3/8 = 7/8. The resulting value (7/8) is less than 1; therefore, this worker's exposure does not exceed the 90 dBA TWA. However, a separate calculation would be required to determine if a hearing conservation program is required.

4. The maximum legal permissible exposure limit (PEL) for noise is _____ for all workers during a 4 hour workday.

a. 80 dBA
b. 85 dBA
c. 90 dBA
d. 95 dBA

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Reducing Noise Hazards

Engineering Controls

Engineering controls are the first line of defense against excessive noise exposure. The use of these controls should aim to reduce the hazardous exposure to the point where the risk to hearing is eliminated or minimized. With the reduction of even a few decibels, the hazard to hearing is reduced, communication is improved, and noise-related annoyance is reduced. There are several ways to control and reduce worker exposure to noise in a workplace.

Engineering Controls
Examples of Engineering Controls
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Engineering controls that reduce sound exposure levels are available and technologically feasible for most noise sources. Engineering controls involve modifying or replacing equipment, or making related physical changes at the noise source or along the transmission path to reduce the noise level at the worker's ear. In some instances the application of a relatively simple engineering noise control solution reduces the noise hazard to the extent that further requirements of the OSHA Noise standard (e.g., audiometric testing (hearing tests), hearing conservation program, provision of hearing protectors, etc...) are not necessary. Examples of inexpensive, effective engineering controls include some of the following:

  • Choose low-noise tools and machinery (e.g., Buy Quiet Roadmap (NASA)).
  • Maintain and lubricate machinery and equipment (e.g., oil bearings).
  • Place a barrier between the noise source and employee (e.g., sound walls or curtains).
  • Enclose or isolate the noise source.

5. Placing a barrier between a noise source and an employee is an example of a(n) _____.

a. physical control
b. hearing protection device
c. engineering control
d. administrative control

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Reducing Noise Hazards

Administrative Controls

Using distance to control exposure.


Controlling noise exposure through distance is often an effective, yet simple and inexpensive administrative control. This control may be applicable when workers are present but are not actually working with a noise source or equipment. Increasing the distance between the noise source and the worker, reduces their exposure. In open space, for every doubling of the distance between the source of noise and the worker, the sound level of the noise is decreased by 6.02 dB. No matter what the scale of measurement, you will get about a 6 dB sound level drop for every doubling of distance. You can see how this works by entering values in the table below.

Open the to calculate the decrease in sound level as distance increases.

There is a risk of exposure to:

Initial distance from sound source  meters or feet
Sound level at the initial distance  dB
Increased distance from sound source  meters or feet
Sound Level at increased distance  dB
Sound level decreased by  dB

Hearing Conservation Program

Hearing protection works only if it's used.

An effective hearing conservation program must be implemented by employers in general industry whenever worker noise exposure is equal to or greater than 85 dBA for an 8-hour exposure or in the construction industry when exposures exceed 90 dBA for an 8 hour exposure. This program strives to prevent initial occupational hearing loss, preserve and protect remaining hearing, and equip workers with the knowledge and hearing protection devices necessary to protect them. For more information on hearing conservation programs, review OSHAcademy Course 751, Hearing Conservation Program Management.

Personal Protective Equipment

Hearing protection devices (HPDs), such as earmuffs and plugs, are considered an acceptable but less desirable option to control exposures to noise and are generally used during the time necessary to implement engineering or administrative controls, when such controls are not feasible, or when worker's hearing tests indicate significant hearing damage.

6. An effective hearing conservation program must be implemented by employers in general industry whenever worker noise exposure is equal to or greater than _____.

a. 45 dBA for a 4-hour exposure
b. 55 dBA for a 6-hour exposure
c. 75 dBA for a 7-hour exposure
d. 85 dBA for an 8-hour exposure

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vibrating tool

Potential Hazards

Vibration caused by machinery is common. Vibration transferred from a machine to the human body may cause discomfort, a reduction of performance, and even injury.

Examples of injury caused by vibration include hand-arm vibration syndrome (HAVS) or damage to the circulatory system of the upper extremities (Raynaud's syndrome).

Vibration may also cause damage to the peripheral nerves (peripheral neuropathy), and to the bones and joints (aseptic necrosis, fatigue fractures, degenerative joint disease).

Open the link to the right for more information: .

Raynaud's Syndrome (also called White fingers) is a disease of the hands in which the blood vessels in the fingers collapse due to repeated exposure to vibration. The skin and muscle tissue do not get the oxygen they need and eventually die.

HAVS is a more advanced condition, and the entire hand or arm may be affected by exposure to vibration.

  • Early signs of HAVS are infrequent feelings of numbness and/or tingling in the fingers, hands, or arms, or numbness and whiteness in the tip of the finger when exposed to cold.
  • As the disease progresses, a worker experiences more frequent attacks of numbness, tingling, and pain and finds it difficult to the hands.
  • A worker with advanced HAVS may be disabled for a long amount of time.

Possible Solutions

Vibration is especially dangerous when proper damping techniques are not applied, if machines are not maintained, if tools are not alternated, or if a worker uses a vibrating tool for consecutive hours during a workday. Possible solutions include engineering controls to remove the vibration hazard and safe work practices to reduce exposure to existing or potential vibration. Workers need to be trained on the hazards of working with vibrating tools, and should always allow the tool or machine to do the work.

Open the link to the right for more information: .

Vibration isolators or damping techniques on equipment offer the most effective protection.

  • Isolate machine vibrations from the surface if it is mounted or by use of vibration isolation mounts.
  • Vibrating panels of machine housings and guards may be controlled by use of damping materials applied to the panels.
  • Felts, liquid mastics, and elastomeric damping sheets are effective damping materials.
  • Determining the correct type and quantity of damping material to use for a particular machine is a complicated process and should be left to a knowledgeable person.
  • The frequency emitted by the machine, the noise reduction level desired, and the weight and size of the machine are factors to consider.
  • A good rule of thumb is that the damping layer should be the same thickness as the surfaces being treated.

Open the link to the right for more information: .

  • Maintain machines in proper working order. Unbalanced rotating parts or unsharpened cutting tools can give off excessive vibration.
  • Arrange work tasks so that vibrating and nonvibrating tools can be used alternately.
  • Restrict the number of hours a worker uses a vibrating tool during the workday. Allow employees to take 10 to 15 minute breaks from the source of the vibration every hour.
  • Train workers about the hazards of working with vibrating tools. Instruction should include: the sources of vibration exposure, early signs and symptoms of hand-arm vibration syndrome, and work practices for minimizing vibration exposure.
  • Instruct workers to keep their hands warm and dry, and to not grip a vibrating tool too tightly. Workers should allow the tool or machine to do the work.

7. Peter frequently works with jack hammers; he has recently been feeling numbness and tingling in his fingers, hands, and arms. These may be early signs of _____.

a. digital neuropathy
b. hand-arm vibration syndrome (HAVS)
c. legionnaires' disease
d. hantavirus

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OSHA Standard: 1915.82, 1926.26, and 1926.56

Potential Hazards:

Inadequate or poor-quality lighting systems can lead to:

  • Slips, trips, and falls.
  • Electric shocks and burns.
  • The inability to exit the space.

Requirements and Example Solutions:

  • Temporary lights must have guards or be recessed to prevent accidental contact with the bulb.
  • Temporary lights must:
    • Be equipped with heavy duty electric cords.
    • templighting
    • Not be suspended by their electric cords.
    • Have splices equal to the insulation of the cable.
  • Cords must be protected from damage.
  • Exposed non-current-carrying metal parts of temporary lights must be properly grounded.
  • Temporary lighting must be equipped with overcurrent protection such as fuses or circuit breakers.
  • In dark areas that do not have permanent or temporary lights, portable emergency lighting such as flashlights or light sticks must be provided.
  • Workers must not enter dark spaces without a suitable portable light.
  • Burning torches should not be used to illuminate work areas.

Construction areas, ramps, runways, corridors, offices, shops, and storage areas shall be lighted to not less than the minimum illumination intensities listed above in the link to OSHA Standard 1926.56 while any work is in progress.

8. Temporary lighting must be equipped with _____ such as fuses or circuit breakers.

a. grounding devices
b. overcurrent protection
c. emergency switches
d. current-limiting devices

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Office Temperature/Humidity

As a general rule, office temperature and humidity are matters of human comfort. OSHA has no regulations specifically addressing temperature and humidity in an office setting. However, Section III, Chapter 2, Subsection V of the OSHA Technical Manual, "Recommendations for the Employer," provides engineering and administrative guidance to prevent or alleviate indoor air quality problems. Air treatment is defined under the engineering recommendations as, "the removal of air contaminants and/or the control of room temperature and humidity." OSHA recommends temperature control in the range of 68-76 degrees Fahrenheit and humidity control in the range of 20%-60%.


Non-Office Work Environments

Operations involving high air temperatures, radiant heat sources, high humidity, direct physical contact with hot objects, or strenuous physical activities have a high potential for inducing heat stress in employees engaged in such operations. Such places include: iron and steel foundries, nonferrous foundries, brick-firing and ceramic plants, glass products facilities, rubber products factories, electrical utilities (particularly boiler rooms), bakeries, confectioneries, commercial kitchens, laundries, food canneries, chemical plants, mining sites, smelters, and steam tunnels.

Outdoor operations conducted in hot weather, such as construction, refining, asbestos removal, and hazardous waste site activities, especially those that require workers to wear semipermeable or impermeable protective clothing, are also likely to cause heat stress among exposed workers.

9. What kind of protective clothing might cause heat stress while working outdoors?

a. any kind of protective clothing
b. insulative or non-conductive
c. semipermeable or impermeable
d. permeable or dark

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Heat (Continued)


Ventilation, air cooling, fans, shielding, and insulation are the five major types of engineering controls used to reduce heat stress in hot work environments.

1. General ventilation

Ventilation is used to dilute hot air with cooler air (generally cooler air that is brought in from the outside). This technique clearly works better in cooler climates than in hot ones. A permanently installed ventilation system usually handles large areas or entire buildings. Portable or local exhaust systems may be more effective or practical in smaller areas.

2. Air treatment/air cooling

Air treatment and air cooling methods differ from ventilation because they reduce the temperature of the air by removing heat (and sometimes humidity) from the air. Air conditioning is a method of air cooling, but it is expensive to install and operate. An alternative to air conditioning is the use of chillers to circulate cool water through heat exchangers over which air from the ventilation system is then passed; chillers are more efficient in cooler climates or in dry climates where evaporative cooling can be used.

3. Fans

Fans cool workers by increasing both the convective heat exchange between the skin surface and the surrounding air and the rate of evaporation. Because this method does not actually cool the air, any increases in air speed must impact the worker directly to be effective.

4. Shields

Shields can be used to reduce radiant heat, i.e. heat coming from hot surfaces within the worker's line of sight. Instead of reducing radiation from the source, shielding is used to interrupt the path between the source and the worker.

5. Insulation

Insulation methods include insulating the hot surface that generates the heat and changing the surface itself. With some sources of radiation, such as heating pipes, it is possible to use both insulation and surface modifications to achieve a substantial reduction in radiant heat.

10. How do fans help to reduce heat stress?

a. Fans increase convection and evaporation
b. Fans cool and move the air
c. Fans decrease the temperature in a room
d. Fans remove heat from the area

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Administrative Controls and Work Practices


Administrative controls employ policies, programs, procedures, and practices to control behaviors that reduce the exposure to heat stress. The following administrative controls can be used to reduce heat stress:

  • Reduce the physical demands of work, e.g., excessive lifting or digging with heavy objects;
  • Provide recovery areas, e.g., air-conditioned enclosures and rooms;
  • Use shifts, e.g., early morning, cool part of the day, or night work;
  • Use intermittent rest periods with water breaks;
  • Use relief workers;
  • Use worker pacing; and
  • Assign extra workers and limit worker occupancy, or the number of workers present, especially in confined or enclosed spaces.


Training is a very important administrative control and the key to safe work practices. Unless all employees gain adequate knowledge, skills, and abilities (KSAs) to use safe work practices when working in stressful temperature conditions, the training program will not be successful. NIOSH recommends that heat stress training program include at least the following components:

  • Knowledge of the hazards of heat stress;
  • Recognition of predisposing factors, danger signs, and symptoms;
  • Awareness of first-aid procedures for, and the potential health effects of, heat stroke;
  • Employee responsibilities in avoiding heat stress;
  • Dangers of using drugs, including therapeutic ones, and alcohol in hot work environments;
  • Use of protective clothing and equipment; and
  • Purpose and coverage of environmental and medical surveillance programs and the advantages of worker participation in such programs.

Hot jobs should be scheduled for the cooler part of the day, and routine maintenance and repair work in hot areas should be scheduled for the cooler seasons of the year.

See OSHAcademy course 602 Heat and Cold Stress Safety for tips to protect workers in extreme temperatures.

11. Reducing the physical demands of work, e.g., excessive lifting or digging with heavy objects, is an example of _____.

a. engineering controls
b. administrative controls
c. mandatory OSHA requirements
d. design controls

Check your Work

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