Chapter 10  

 Physical Hazards

Physical agents are forms of energy that can harm the body when exposure takes place. They include mechanical energy which impacts on the body from noise and vibration. Other physical agents include hot and cold temperatures which can affect the body's normal internal temperature. Some forms of radiation may affect the body's cells. They may be a specific part of the production process or an unwanted byproduct. Exposure to excessive noise or vibration, extreme temperatures and radiation can lead to acute or chronic health effects.

Excessive noise levels may be hazardous. Loud or prolonged noise can damage the sensitive nervous tissue in the ear, resulting in temporary or permanent hearing loss.

Vibration may affect the whole body, but more frequently this hazard involves hand-arm vibration from using hand-held power tools. Some types of vibration may damage the small blood vessels and nerves in the hands, while others can cause back pain.

Temperature is considered extreme when it falls outside the range where the human body can easily maintain its normal internal temperature. Workers may be exposed to extreme temperatures when working outside, near furnaces or stoves, in refrigerated workspaces, or in loading areas with open doors. Extreme temperatures put the body under stress as it struggles to maintain its normal internal temperature.

Radiation is electromagnetic energy which radiates in waves. Radiation may damage the skin or the eyes, as well as damage the cells and cause cancer.

Each of these physical hazards has specific health effects. The methods of exposure assessment and types of control are also specific to each hazard. This chapter discusses each of them separately.

Noise is unwanted sound. Sound is a form of mechanical energy caused by the vibration of the air. When sound vibrations reach the listener they are detected by a delicate mechanism in the inner ear and perceived as sound by the brain. Sound has three principal characteristics: frequency, amplitude and time pattern. 

Frequency is perceived as pitch. It is the rate at which the sound waves are vibrating. A high-pitched sound is one with a high frequency. Frequency is usually measured in cycles per second, or Hertz. Normal speech is in the 250 to 4,000 Hertz range.

Amplitude is perceived as loudness. It is the strength of the sound signal being received. The human ear is responsive to a very wide range of sounds. Amplitude is measured in decibels (dB). A decibel is one-tenth of a bel. The decibel scale is logarithmic rather than linear. This means that if there is an increase of one bel, the sound is ten times louder than before. The use of a logarithmic scale makes it possible to describe a very wide range of sound amplitudes.

Time pattern refers to the continuity and fluctuation of a sound. Continuous noise is that produced constantly. Impulse noise consists of separate pulses, which may or may not repeat a pattern and can have higher and lower sound levels.

Health Effects of Noise

Excessive noise has the potential to impair hearing, or even destroy it. Noise may also put stress on other parts of the body causing the abnormal secretion of hormones, the tensing of muscles and other health effects. Sleeplessness and fatigue are among the symptoms. Noise also interferes with communication, which can affect normal functions including job performance and safety. The specific health effects depend on the type of noise involved and the duration of the exposure. To help understand these effects, it will be useful to briefly review the hearing mechanism.

Hearing begins when the outer ear collects and funnels sound waves to the eardrum through the pinna canal. The eardrum vibrates as it receives the sound waves. The vibrations are transmitted through three small bones: the hammer, the anvil and the stirrup in the middle ear.

The middle ear acts as an amplifier. The stirrup sits on the end of a flexible membrane called the oval window. The oval window separates the middle ear from the inner ear which contains the hearing organs.

Attached to the other side of the oval window is a tiny, fluid-filled, snail-shaped structure called the cochlea. The fluid inside the cochlea is set in motion by vibrations intercepted at the oval window. The vibrations are then transferred to thousands of very small, very sensitive, hair-like cells resembling bristles. Each one connects with microscopic nerve endings that send messages to the brain, where the signals are interpreted as sound.

Hearing Loss

A hearing loss is any reduction in the normal ability to hear. A hearing loss can be temporary or permanent and it might be partial or total. Immediate and permanent damage to the ear can result from acoustic trauma when a person is exposed to a sudden and excessive noise, such as an explosion. This can cause damage to the delicate tissues of the middle ear. Prolonged exposure to continuous elevated noise can cause damage that is more gradual, but in the long run may be just as damaging. Noise-induced hearing loss, once established, is not reversible.

There is a natural hearing loss due to the normal aging process, which is called presbycusis.

Threshold Shift

A threshold shift is the loss of a person's ability to hear higher frequency sounds. It results from damage to the cochlea. The tiny hairs of this organ, or the nerves they are connected to, can be damaged by prolonged exposure to noise. The hair-like cells which are most receptive to the higher frequencies are often the first to go. This is true even if the noise that caused the damage was at a lower frequency. The most vulnerable hair-like cells are those responding to the 4,000 Hertz range.

The first symptom of a threshold shift is a loss of hearing at the higher frequency levels. In speech, the first sounds missed are the consonants s, f, t, p and k, which have relatively high frequencies. Yet vowels may be heard normally. As the damage progresses, hearing loss extends into the lower frequencies, and poor understanding of speech becomes more apparent. A threshold shift can be permanent or temporary.

A temporary threshold shift can convince some people that they have become used to the noise. Intense noise, now perceived at a lower level, may continue to damage hearing and may result in permanent hearing loss. Tinnitus, or ringing in the ears, is one sign that exposure to noise has been excessive. It may be permanent or temporary.

With a temporary threshold shift, normal hearing will usually return after a period away from noise. The fluid in the inner ear may be changed by noise, but can revert to its original composition. The time needed for recovery depends on the severity of the initial loss.

An example of a temporary threshold shift might be a worker who has to turn up the volume on the car radio on the way home from work. The sound level that was adequate on the way to work in the morning is now difficult to hear.

Assessing Noise Exposure

A workplace inspection will usually reveal any areas with high noise levels. Inspections may have to be done at different times to ensure that all noise sources are identified. If it is difficult to carry on a conversation noise levels may exceed safe limits. The employer or JHSC member should ask workers whether they have had any problems associated with noise. Common sources of noise include machinery, ventilation systems and power tools.

Sources of noise could be specified on a floor plan, and the workers who may be exposed can be identified. Existing noise controls should also be identified. The next step is to assess the amount of exposure. Exposure assessments or sound level measurement should be conducted periodically in order to evaluate the effectiveness of controls.

Several different types of instrument are available for assessing noise levels. The sound level meter is the most useful. Others include noise dosimeters and frequency analyzers.

Sound Level Meter

Sound Level Meters

A sound level meter consists of a microphone, an amplifier and an indicator gauge. Standard meters incorporate three different weighting systems, to approximate the varying response of the human ear to various frequencies. An "A" weighted sound level, or dBA, comes the closest to approximating human responses. The action of the meter can be adjusted to "fast" or "slow". A slow setting averages intermittent or variable sounds. The sound level meter needs to be calibrated regularly, preferably before and after each use. This ensures the accuracy of the sound measuring equipment.

Noise Dosimeters

In many work environments, workers move from location to location throughout their shift. Each location may have a different noise level. The noise exposure of the individual worker can be measured with a noise-exposure monitor, or dosimeter. It is worn by the worker and records the total noise energy that the worker is exposed to, preferably for a full work shift.

Noise Dosimeter

Frequency Analyzers

When designing noise control devices it is important to know the frequency distribution of the noise. Different sound-absorbing materials work best in specific frequency ranges. An octave band or frequency analyzer is used to provide this information. It may also be used to determine a source of noise.

Survey Techniques

A noise exposure survey is a systematic approach to measuring noise level exposures in the workplace. CSA Standard Z107.56-M1986 provides information on methods of taking and interpreting sound measurements. Readings of sound level, duration and time pattern are required. They are taken at locations where workers may be exposed. Sound level readings are usually taken first to get an overall picture of where noise is generated. Then, if needed, dosimetry may also be carried out. It is essential that equipment be properly calibrated and operated by qualified persons. Professional consultants are usually brought in to conduct an assessment.

Controlling Noise

Noise can be controlled at the source, along the path or at the worker. At the source, equipment may be replaced by quieter models, or less noisy work procedures can be adopted. In general, less friction and vibration mean less noise. Maintenance procedures such as lubrication may sometimes reduce noise by reducing friction. Equipment can sometimes be modified to reduce the amount of noise that is generated. Sound-absorbing material may be attached to the noise source. Or the frequency of the noise may be shifted to one that is less hazardous.

Noise can often be controlled along the path to the worker with the use of sound-absorbing paneling on walls or ceilings, and enclosures around noisy machinery.

Controls at the worker include both administrative controls and personal protective equipment. Administrative controls modify how the work is carried out. The time employees spend in noisy areas may be reduced. Workers in noisy areas may be rotated to less noisy areas.

Noisy operations may be conducted outside normal working hours to reduce the number of people exposed.

Where noise exposures cannot be reduced by other methods, hearing protection is required. This includes ear plugs and ear muffs. Hearing protection devices must be properly fitted and must be appropriate for the level, frequency and duration of the noise involved. CSA Standard Z94.2-M1984 provides guidelines for selecting and using hearing protection. Everyone in the workplace should wear hearing protection when the sound level is greater than 90 dBA for any period of time.

Vibration is a rapid alternating or reciprocating motion. It can affect all or part of the body. For example, driving a tractor over bumpy roads in a poorly designed seat vibrates the entire body. Prolonged use of a vibrating hand tool can affect the hands and arms.

Health Effects of Vibration

The energy from vibration is absorbed by the tissues and organs of the body. Whole body vibration can lead to lower back pain. Hand-arm vibration causes damage to blood vessels, impairing circulation in the hand. This leads to a condition known as white finger, or Reynaud's phenomenon. When exposed to cold, the hands appear to be mildly frostbitten. The damage can progress to the point where it disables the victim. White finger disease is most common among operators of air hammers, air chisels and chain-saws.

Vibration Monitoring

The evaluation of exposure to vibration is very technical. In general, the harm caused by vibration increases with its strength and with the duration of exposure. Exposure values have only recently been developed, and are intended primarily for use by experts equipped with sophisticated equipment.

Certified members can make a preliminary assessment of vibration problems by talking with workers and observing the work. For example, the workplace floor may vibrate. Workers who use hand tools may report problems with their hands. A vibration specialist might be consulted to obtain a more accurate assessment of the problem.

Controlling Vibration

Vibration can be controlled at the source by redesigning the equipment to include vibration-absorbing mounts or shock absorbers. Older equipment can be replaced with newer vibration-free models. Control along the path involves the use of vibration-absorbing handles and vehicle seats, or remote control systems. Vibration-absorbing gloves are the most common form of control at the worker.

The human body functions efficiently only within a very narrow range of internal temperatures. The normal deep body temperature is 37.6 degrees Celsius. The temperature at the mouth is a little lower, about 37 degrees. If the deep body temperature falls below 36.4 degrees or rises above 39.2 degrees, body functions are significantly impaired.

The body has automatic systems that maintain internal temperature within this narrow range under normal circumstances. If the body gets overheated, blood flow to the skin is increased to radiate heat. Sweat flows on the surface of the skin. When it evaporates, the body is cooled. If the body is too cold, capillaries in the skin constrict, to reduce blood flow to the skin. Involuntary shivering causes muscles to burn stored energy and release heat. If the body is exposed to excessive temperatures for prolonged periods, these automatic heating and cooling systems get overloaded, and the body is placed under stress.

Exposure to Heat

High temperatures are encountered in many workplaces. Often the heat source is part of the work process, as in a steel mill or a laundry. In the summer, outdoor temperatures can reach 35 degrees, creating a possible hazard for some people working outside. If the body's cooling system is overloaded, the body is placed under heat stress.

Health Effects of Heat Stress

The health effects caused by heat stress include heat cramps, heat exhaustion and heat stroke. Heat stress can also increase the risk from other health and safety hazards.

Heat cramps are caused by loss of fluid and body salts, sometimes in combination with heavy exertion. They can be very painful and affect several different muscle groups. Heat exhaustion results from the depletion of body fluid and salts. The symptoms include dizziness, nausea and profuse sweating. Heat stroke is the failure of the body's temperature regulating system, leading to a rise in body temperature that can cause death.

Assessing Heat Exposure

Exposure to excessive heat can be recognized by a number of means. These include measuring temperature and humidity. Information about heat exposure can also be obtained by talking to workers and supervisors. If workplace heat is making them uncomfortable, further assessment may be necessary.

The assessment of heat exposure must take into account both temperature and humidity. High humidity hampers the body's ability to cool down by sweating, because sweat does not evaporate as quickly. The hazard from heat stress is also increased by radiant heat. Assessment should also take into account any acclimatization to heat a person may have acquired after a period of exposure.

The Wet Bulb Globe Temperature Index (WBGT) is a commonly used indicator for measuring the conditions that may cause heat stress. It is calculated with a formula that takes into account three different temperature measurements:

• The Dry Bulb temperature is measured by an ordinary thermometer.
• The Natural Wet Bulb temperature is measured by a thermometer which has the reservoir at the bottom encased in a wetted cloth. It measures the effect of humidity.
• The Globe Thermometer temperature is measured by a thermometer encased in a black sphere or "globe". It measures the effect of radiant heat.

An electronic device is available that will measure all three indicators at the same time.

Many health and safety specialists use the Threshold Limit Values (TLVs) developed by the American Conference of Governmental Industrial Hygienists (ACGIH). The suggested TLVs for continuous work are a WBGT of 25 degrees for heavy work, and a WBGT of 30 degrees for light work.

Controlling Heat Exposure

Heat exposure can be controlled at the source by redesigning equipment and work processes. Examples include insulating and isolating heat sources. Control along the path includes ventilation or air conditioning to reduce air temperature and reflective barriers to reduce radiant heat.

There are several types of control at the worker. Work can be scheduled to provide work/rest cycles and worker rotation. Climate-controlled booths can protect equipment operators. And special clothing such as body-cooling vests and insulated or reflective clothing can also help to control heat stress. Provision should also be made for drinking water.

Exposure to Cold

Workers are exposed to cold when they work outdoors or in refrigerated indoor environments. Workers in construction, forestry, utilities and food processing and storage are most often affected. Working for prolonged periods in cold environments causes the body to decrease blood flow to the skin. The result can be cold stress.

Health Effects of Cold Stress

The immediate health effects of cold stress are restlessness, decreased alertness and lack of concentration. Performance of complex manual and mental tasks is impaired. Numbness and weakness may contribute to other health and safety hazards. In particular, a worker may become more vulnerable to injuries of the musculoskeletal system, such as muscle strain. If exposure is prolonged or extreme, frostbite or hypothermia may result.

Frostbite is the freezing of body tissues. The fingers, toes, ears and nose are particularly vulnerable. Skin freezes at about -1 degree Celsius. If it is windy, this can happen quickly. Exposed flesh can freeze in about one minute at -10 degrees with a wind of 12 kilometres per hour. Frostbite can also be caused by contact with cold objects.

Hypothermia results when the body mechanisms can no longer maintain internal temperature above 35 degrees. Blood vessel constriction is no longer adequate to retain heat and shivering becomes the only mechanism available.

Assessing Cold Exposure

Moving air greatly increases heat loss from the body. For this reason, exposure to cold temperatures is usually evaluated according to the wind chill index. This is a combination of air temperature and wind speed. It can be calculated from a wind chill table.

The ACGIH has suggested Threshold Limit Values (TLVs) for cold stress. The TLVs are organized by temperature and wind speed, and provide work/warmup schedules for a four-hour period. For example, at -30 degrees Celsius, only one break would be needed for moderate-to-heavy work if there were no wind. But four breaks would be needed in a 15-mph wind and the maximum work period would be 40 minutes in a four-hour shift.

  Wind-chill Effect

Controlling Cold Stress

Control at the source is not generally possible outdoors. Indoors, it may be possible to reduce the number of workers exposed by modifying, enclosing or isolating cold areas. In refrigerator rooms, cold can be controlled along the path by minimizing air velocity as much as possible. Insulated clothing is a form of control at the worker.

Outdoor controls are mainly at the worker. These include insulated wind-protective clothing, including mitts or gloves. Work practices should include a work/warmup cycle according to the ACGIH guidelines. Temporary shelters and other warmup areas may be provided.

Radiation is the emission or transmission of energy as waves or moving particles. Although we are not often aware of it, radiation is absorbed by the body where it can affect the tissues and cells and lead to a variety of health effects.

Radiation can be divided into two main types: ionizing and non-ionizing. Ionizing radiation is at the high frequency end of the electromagnetic spectrum, which means that it has the shortest wavelengths. Ionizing radiation is considered the most harmful to humans.

Ionizing Radiation

Ionizing radiation is produced by the natural decay of radioactive elements such as uranium. It has enough power to strip electrons from atoms and cause ionization. This can interfere with the body's cellular structure and cause genetic damage.

Ionizing radiation is produced by such devices as X-ray machines. There are several kinds of radiation and a complete description of them is beyond the scope of core certification training. Different forms of radiation may have different routes of entry into the body. A particular concern in many workplaces is Gamma rays, which for practical purposes can be considered the same as X-rays. Workers in radiology departments are potentially at risk to exposure to X-rays from the equipment they use.