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	worker at table saw with hood and guard

Input: Occupational Safety and Health Risks

Disease, injuries, and fatalities among the nation’s workers are substantially reduced with the proper use of engineering controls. Engineering controls can reduce occupational risks across all sectors of the workforce by reducing harmful exposures. The following list contains a few examples of how NIOSH Engineering Control Research has been successful in documenting the reduction of harmful worker exposures in various industries, up to:

  • 99% of cough aerosols in isolation beds in the healthcare industry
  • 99% of volatile compounds during flavorings production activities
  • 99% of carbon monoxide from marine vessels
  • 90% of respirable dust during jack hammer operations on concrete
  • 80% from asphalt fumes during road paving

The risk of developing a work related disease, injury, or fatality is reduced when engineering controls are used to control hazards below occupational exposure limits (OELs). In evaluating the hazards posed by workplace exposures, NIOSH investigators use mandatory and recommended OELs for specific chemical, physical, and biological agents. Generally, OELs suggest levels of exposure to which most workers may be exposed up to 10 hours per day, 40 hours per week for a working lifetime without experiencing adverse health effects. It is, however, important to note that not all workers will be protected from adverse health effects even though their exposures are maintained below these levels. A small percentage may experience adverse health effects because of individual susceptibility, a pre-existing medical condition, and/or hypersensitivity (allergy) to the specific hazardous substance. In addition, some hazardous substances may act in combination with other workplace exposures, the general environment, or with medications or personal habits of the worker to produce health effects even if the occupational exposures are controlled at the level set by the exposure limit. Combined effects are often not considered in the OEL. Also, some substances can be absorbed by direct contact with the skin and mucous membranes in addition to being inhaled, thus contributing to the overall exposure. Finally, OELs may change over the years as new information on the toxic effects of an agent become available.

Most OELs are expressed as a time-weighted average (TWA) exposure. A TWA refers to the average exposure during a normal 8- to 10-hour workday. Some chemical substances and physical agents have recommended short-term exposure limits (STEL) or ceiling values where there are health effects from higher exposures over the short-term. Unless otherwise noted, the STEL is a 15-minute TWA exposure that should not be exceeded at any time during a workday, and the ceiling limit is an exposure that should not be exceeded at any time, even instantaneously.

In the U.S., OELs have been established by Federal agencies, professional organizations, state and local governments, and other entities. Some OELs are mandatory, legal limits; others are recommendations. The U.S. Department of Labor OSHA PELs [29 CFR 1910 (general industry); 29 CFR 1917 (maritime industry); and 29 CFR 1926 (construction industry)] are legal limits that are enforceable in workplaces covered under the OSH Act. NIOSH recommended exposure limits (RELs) are recommendations that are made based on a critical review of the scientific and technical information available on the prevalence of hazards, health effects data, and the adequacy of methods to identify and control the hazards. Recommendations made through 1992 are available in a single compendium [NIOSH 1992]; more recent recommendations are available on the NIOSH Web site . NIOSH recommends preventive measures (e.g., engineering controls, safe work practices, personal protective equipment (PPE), and environmental and medical monitoring) for reducing or eliminating the adverse health effects of these hazards. The NIOSH Recommendations have been developed using a weight of evidence approach and formal peer review process. Other OELs that are commonly used and cited in the U.S. include the threshold limit values (TLVs®) recommended by the American Conference of Governmental Industrial Hygienists (ACGIH®), a professional organization [ACGIH® 2007]. ACGIH® TLVs® are considered voluntary guidelines for use by industrial hygienists, engineers, and others trained in this discipline “to assist in the control of health hazards.” Workplace environmental exposure levels (WEELs) are recommended OELs developed by American Industrial Hygiene Association (AIHA), another professional organization. WEELs have been established for some chemicals “when no other legal or authoritative limits exist” [AIHA 2007].

Employers should understand that not all hazardous chemicals have specific OSHA PELs and for many agents, the legal and recommended limits mentioned above may not reflect the most current health-based information. However, an employer is still required by OSHA to protect their employees from hazards even in the absence of a specific OSHA PEL. In particular, OSHA requires an employer to furnish employees a place of employment that is free from recognized hazards that are causing or are likely to cause death or serious physical harm [Occupational Safety and Health Act of 1970, Public Law 91–596, sec. 5(a)(1)]. Thus, NIOSH investigators encourage employers to make use of other OELs when making risk assessment and risk management decisions to best protect the health of their employees. NIOSH investigators also encourage the use of the traditional hierarchy of controls approach to eliminating or minimizing identified workplace hazards. This includes, in preferential order, the use of:

  1. substitution or elimination of the hazardous agent,
  2. engineering controls (e.g., local exhaust ventilation, process enclosure, dilution ventilation),
  3. administrative controls (e.g., limiting time of exposure, employee training, work practice changes, medical surveillance), and
  4. personal protective equipment (e.g., respiratory protection, gloves, eye protection, hearing protection).

The best way to reduce the risk of occupational injury, illness, or fatality is through elimination or substitution of the hazard. In situations where elimination or substitution of the hazard is not possible, engineering controls are an effective way to reduce occupational risk of disease, injuries, and fatalities. The best time to implement an engineering control is during the design phase of a new facility, equipment, or process. Engineering controls should focus on controlling the hazard at or near the source. When possible, the hazard should be completely enclosed to prevent exposure through normal operations. When complete enclosure is not possible, barriers or local ventilation should be used to reduce the occupational risk by reducing exposure to the hazard during normal operation.


ACGIH® [2007]. 2007 TLVs® and BEI s®: threshold limit values for chemical substances and physical agents & biological exposure indices. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

AIHA [2007]. 2007 Emergency Response Planning Guidelines (ERPG) & Workplace Environmental Exposure Levels (WEEL) Handbook. Fairfax, VA: American Industrial Hygiene Association.

NIOSH [1992]. Recommendations for occupational safety and health: compendium of policy documents and statements . Washington, DC: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 92-100.