Nicole Matoushek PT MPH CSHE CEES
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Joined: January 15, 2005
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Environmental Risk Factors
A risk factor is an attribute, experience or exposure that increases the probability of the occurrence of a disease or disorder. Though the presence of a risk factor does increase the likelihood of disease occurrence, a risk factor is not necessarily a causal factor. Environmental risk factors are factors that are from the environment and they can attribute to the development of work-related injuries, however, they are not always easily modified or under the control of the worker. Environmental factors include: vibration, thermal stress, lighting and noise exposure.
Acceptable Exposure Limits/Threshold Limit Values
In order to protect workers from injury from exposure to environmental risk factors, guidelines or acceptable exposure limits have been developed. Both the Occupational Safety and Health Administration (OSHA) and the American Conference of Governmental Industrial Hygienists (ACGIH) have documented hazard exposure limit values. OSHA has developed Permissible Exposure Levels (PELs). PELs are the recommended, allowable, maximal exposure values. PELs can be used as legal standards.
The ACGIH has developed Threshold Limit Values (TLVs). These threshold limit values refer to exposure values under which it is believed that nearly all workers may be repeatedly exposed day after day without adverse health effects. TLVs are developed as guidelines for exposure limits and they are in place to assist in the control of environmental health hazards. They are not developed for use as legal standards, but are used to assist in making recommendations for worker safety and health.
Vibration
Vibration is defined as the oscillatory motion of a body or body segment. Vibration is the back and forth, linear motion that an object experiences, as it moves from and returns to, some defined stationary point of reference.
Human Body Vibration Frequencies
These physical characteristics of vibration are important, in that the body receiving the vibration can actually experience an amplification of intensity of the vibration, thus exacerbating the effects. This occurs when the frequency of the body part receiving the vibration is similar or close to the range of frequency of the vibration source. The human body is essentially a system of tissues joined by dampers and springs. All parts of the human body vibrate at specific, yet different frequencies. These frequencies range from 2-100 Hz. If the body is exposed to a new, externally applied frequency, and this frequency is of similar frequency of the body, then the intensity becomes magnified, and the affect of the vibration is amplified. The affects from vibration represent a type of cumulative trauma to the exposed tissues. Vibration stress affects multiple body parts and organs. The duration of exposure, the direction and intensity of the vibration are all important factors when considering vibration in the workplace. In the occupational setting, a worker can experience exposure to vibration simultaneously in more than one frequency (Hz). This vibration experienced at work, can be either whole body vibration or segmental vibration.
Whole Body Vibration
Whole body vibration (WBV) is when the entire body is exposed to the same vibration frequency. Most frequently, the vibration is transmitted to the entire body through some supporting structure. The human body tolerates whole body vibration better when in the standing position, as opposed to the sitting position, and women tend to experience more discomfort than men, on average, when exposed to the same vibration source. The duration of exposure, as well as the acceleration and frequency characteristics of the vibration source will determine the level of discomfort or tolerance of the worker.
Methods for Risk Factor Control: WBV
Possible methods to control Whole–body vibration may include;
· The utilization of suspended seating systems, such as suspended cabs. This will isolate the vibration source from the worker.
· Maintain vehicle suspension systems. Regular scheduled maintenance will ensure that the equipment is working properly, and identify when new suspension systems are needed.
· Provide adequate tire inflation. Proper tire inflation will attenuate the vibration.
· Install a remote control system for the operation of vibration producing work processes. This will reduce the exposure of the worker to the vibration source.
· Promote good working positions that will help attenuate whole-body vibration. Maintaining neutral joint positions during the vibration exposure and avoiding lifting or bending immediately following the vibration exposure will reduce the adverse effects from exposure to vibration.
· Allow a longer recovery period to the exposed tissues.
· Provide Vibration absorbing materials to the work place. These can include: rubberized anti-vibration mats or gel shoe inserts.
Segmental Vibration
Segmental vibration (SV) exposure is when only a specific body segment is exposed to the vibration source. Most often this occurs to the upper extremity when using power tools or industrial machinery. The range of frequency of SV, which is most often observed in industry, is the range between 5-5000 Hz. Vibration frequencies of greater than 250 Hz can contribute to the magnitude of the vibration exposure. However, most of the common causes of micro-trauma injuries from hand-transmitted vibration are frequencies of less than 250 Hz. For Hand-Arm vibration sources, accelerations in the range of 1.5(g) to 80(g), and vibration frequencies in the range of 8 to 500 Hz produce the greatest exposure risk. This means that exposure to SV of this range has the potential to cause the most severe adverse health effects.
Methods for Risk Factor Control: SV
Possible methods to control segmental vibration may include:
The utilization of fastener or dampening devices. These fasteners and dampeners may reduce the drive of the tool, thus reducing the exposure to vibration.
The use of attenuation covers and Personal Protective Equipment (PPE). These protective coverings reduce vibration exposure by providing a barrier between the worker and the exposure. Examples include: gel packed gloves, gel shoe inserts.
Ensure regular tool and balance maintenance.
Ensure that regular sharpening is performed to the equipment such as grinders or cutting tools.
Increasing the Revolutions per Minute (RPM) or cycle time of a power tool. Increasing the RPMs can also help to lessen the vibration intensity.
Thermal Stress
Thermal stress is the stress to the human body due to exposure to temperature extremes. Both heat exposure and cold exposure are important to consider. In both cases, exposure to temperature extremes or thermal stress can lead to overexertion injury and even death.
The temperature of a workplace or work area can affect worker performance, worker efficiency, and increase the likelihood of overexertion due to fatigue, thus leading to the higher risk of developing a cumulative trauma injury. Hot and humid work environments place higher physical demands on work tasks that involve moderate to heavy workloads. Hot and humid temperatures cause excessive fatigue and overexertion by adversely affecting the worker’s work capacity. Cold temperature environments can lead to increased exertion, lower worker efficiency and reduced finger tactility where finger manipulation or grasping functions are required. This results in a greater likelihood of overexertion to the muscles and tendons of the hand and arm. In addition, exposure to hot and cold temperatures may require the use of additional or fewer protective clothing. This can lead to difficulty with mobility, trip and fall hazards, or cause a distraction for the worker; this in effect can result in an unsafe act or cause injury.
Methods for Risk Factor Control: cold stress
Methods to control cold stress include:
Providing adequate insulating dry clothing to maintain core temperatures above 36 degrees C (96.8 degrees F). This additional clothing, actually used as Personal Protective Equipment, may in itself lead to poor dexterity or trip and fall hazard, therefore proper training of the workers is recommended.
If fine manipulation or dexterity tasks need to be performed with bare hands for more than 10-20 minutes in an environment below 16 degrees C (60.8 degrees F), then special provisions should be supplied to workers to keep their hands warm and allow adequate circulation. These controls can include: warm air jets, radiant heaters, or warming plates.
Metal tools can be covered by thermal insulating materials.
Gloves should be used in cold environments when ever feasible.
Reduce airflow or ventilation, by providing or construction windshields or barriers.
If cold stress cannot be controlled sufficiently with these methods, job rotation and warm up periods should be allowed.
Methods for Risk Factor Control: heat stress
Methods to control adverse health effects from heat stress exposure include:
Provide adequate ventilation. This can be accomplished by increasing airflow with industrial fans.
Evaluate and if necessary, provide the appropriate clothing. Clothing should be loose fitting, light in weight and color, as to not absorb more heat, and made from thin and breathable materials like cotton.
Job rotation is an effective means of limiting exposure times.
Additional rest or recovery periods may be recommended. In certain circumstances when additional Personal Protective Equipment is required, as in the case of chemical handling, these precautions may need to be increased.
Illumination
Illumination is defined as a measure of the amount of light. Light levels are measured by an illumination meter in units of lux or footcandles. The meter is set directly at the work surface. In general, the further away the illumination meter is from the light source, the lower the illumination level. Luminance, is a measure of light reflected off of a work surface, it is associated with “brightness”. The luminance or brightness of an object or work surface does not change as the distance from the light source changes. The level and quality of illumination, or lighting will directly influence a workers ability to perform his or her job efficiently. In addition, eye and muscle strain can result if straining is required in conditions of insufficient lighting. Luminance, or the brightness of an object can also affect a worker’s performance. If the brightness is excessive, it can distract or cause strain to a worker. Therefore, lighting exposure is an essential factor to consider when evaluation environmental risk factors.
Methods for Risk Factor Control
Control measure to ensure proper lighting is used include:
Provide additional task lighting when high visual acuity is required.
Minimize both indirect and direct glare.
CControl for direct glare. As it appears feasible, position the light source as far away from the worker’s visual line of sight. Use multiple low level light sources instead of one bright source. Use indirect lighting. Use light shields or reflectors.
Control for indirect glare. Provide work surfaces that diffuse reflected light. Position light sources away from worker.
When using Video-Display Units (VDU), utilize anti glare screen or antireflection coatings for computer monitors.
When using VDUs, change the work area to avoid indirect glare in the monitor. This can be accomplished by: lowering the general lighting, covering windows with blinds or draperies, tilt the computer screed downward, orient the work area such that the worker is sitting with his or her back towards a dark colored wall, avoid having the back facing a window, or other objects that will reflect light such as doors and pictures.
Sound and Noise
Sound is a wave of mechanical energy. Sound is an organized movement of molecules that is sent out from a source, and propagates as a series of pressure waves through a medium of air or water. The energy that propagates through air as a sound wave travels at a velocity of 340 m/s (1100 ft/sec). Sound is an auditory sensation produced by the ears following an alteration in pressure and movement of molecules as a result of the sound pressure wave. Noise is defined as an annoyance factor of sound.
Methods for Risk Factor Control
Methods to reduce noise levels in the work place, to prevent NIHL and enhance worker performance include:
Implementing noise control programs.
Implementing hearing conservation programs, to include annual hearing testing.
Utilizing barriers or sound absorbing materials to protect workers form the noise exposure.
Utilizing Personal Protective Equipment such as ear plugs and muffs to reduce individual noise exposure.
Summary
Environmental risk factors are factors in the work environment that are found to contribute to the development of Cumulative Trauma Disorders (CTDs) in the work place. Environmental risk factors that are important in Health Ergonomics include: vibration, thermal stress, lighting, sound and noise exposure. Careful identification and evaluation of these environmental factors is essential to the Ergonomics process. Whenever possible, utilizing the proper control methods will help to reduce the exposure of the risk. And by controlling the risk, the potential for the development of CTDs in the workplace are reduced.
_____________________________
Nicole Matoushek, PT, MPH, CSHE, CEES
http://www.ErgoRehabinc.com
http://www.ErgoRehabBlog.com
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