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Anyone that has been in a high school chemistry laboratory has no doubt noticed the numerous postings stressing laboratory safety.  While there are both physical and chemical hazards in these laboratories, it’s toxicologists that provide information involving hazardous chemicals.  The chemistry lab is a short term experience for the student, but it’s the workplace for the instructor.  Indeed, potentially hazardous chemicals are used in many workplaces.

In 1973, Stellman and Daum called the “workplace” a battleground in the war against poisonous chemicals and dangerous working conditions.  Chemical hazards can involve any number of substances including solvents, heavy metals, petroleum, etc.  Since exposures are often inevitable, preparing and protecting workers from the toxicological consequences of such exposures is imperative. The tools for protecting workers are many. Information, derived from sound science-based standard setting, is the crucial component of occupational safety and health – the knowledge and application of that information makes for a safer workplace.

Fifty years ago, the Occupational Safety and Health Act of 1970 was enacted to ensure safe and healthful working conditions for all workers. It empowered two federal agencies to oversee and contribute to worker safety: 1) The Occupational Safety and Health Administration (OSHA) in the Department of Labor and 2) the National Institute for Occupational Safety and Health (NIOSH) within the Centers for Disease Control and Prevention (CDC). OSHA protects the workforce by setting and enforcing standards and by providing training, outreach and education.  NIOSH conducts research to identify and update our knowledge about workplace hazards and ways to improve safety practices for the protection of workers.

Prior to 1970 and the creation of OSHA and NIOSH, the American Conference of Government Industrial Hygienists ACGIH®, a 501(c)(3) charitable scientific organization, was founded to  “to encourage the interchange of experience among industrial hygiene workers and to collect and make accessible such information and data as might be of aid to them in the proper fulfillment of their duties.”  The ACGIH still plays an important role today in helping to set and execute safe practices for workplace exposure.

Identifying Workplace Hazards:

NIOSH toxicologists identify hazards and develop recommended procedures that allow a worker to use a chemical safely.  This includes not only new hazards, but new ways to better protect workers from known hazards.   The NIOSH Pocket Guide to Chemical Hazards (NPG) informs workers, employers, and occupational health professionals about workplace chemicals and their hazards. The NPG gives general industrial hygiene information for 677 chemicals/classes.  The guide also offers key facts designed to help users recognize and control workplace chemical hazards.

Setting Standards for Workplace Exposures:

As noted, OSHA sets and enforces protective workplace standards. These standards provide safe limits of the amount of hazardous chemicals workers can be exposed to, establishes safe practices and equipment, and requires employers to keep records of workplace injuries and illnesses. In the US, exposure standards are called Occupational Exposure Limits (OELs).  OEL’s are defined as the upper limit on the acceptable concentration of a hazardous substance in workplace air for a particular material or class of materials. They are established with the input of ACGIH, NIOSH, and OSHA, but enforced by OSHA only. Because numerous agencies help develop OELs, there are agency-specific terms that each group uses in defining permissible exposures.  For example, the Permissible Exposure Limit (PEL) is used by OSHA.  The Recommended Exposure Limit (REL) is used by NIOSH and the Threshold Limit Value (TLV) is used by ACGIH. While the acronyms can be confusing, all are basically measurements that identify the upper exposure limits of a hazardous substance based on 8 hours of exposure.   More information on each can be found in the appendix.

Health Hazard Evaluations (HHE):

An employer, employee, or union official in a workplace where employees’ health and well-being may be affected by chemical exposure can request an HHE. If justified, NIOSH goes to the workplace and evaluates the current workplace conditions and employee health concerns and makes recommendations on how to reduce or eliminate any identified hazards.

Hazard Communication with Employees—Posters and Safety Data Sheets:

To communicate hazard information, the OSHA Hazard Communication Standard (HCS) requires the chemical manufacturer, distributor, or importer to provide Safety Data Sheets (SDSs) (formerly Material Safety Data Sheets) for each hazardous chemical to users. The information contained in the SDS is presented in a consistent user-friendly, 16-section format.

The SDS includes information such as the properties of each chemical; the physical, health, and environmental health hazards; protective measures; and safety precautions for handling, storing, and transporting the chemical. The information contained in the SDS must be in English (although it may be in other languages) and because the information might be necessary in an emergency situation, employers must ensure that SDSs are readily accessible to employees.

Global Workplace Protection:

Because the economic and social costs of worker injuries and deaths are staggering, protecting workers is a global concern. Many countries have laws and government regulatory agencies similar to the U.S. organizations to regulate and address issues related to workers’ exposure to dangerous agents and situations. In the European Union, the European Agency for Safety and Health at Work is the primary agency concerned with occupational safety and health.  The World Health Organization’s (WHO) website notes that “occupational health deals with all aspects of health and safety in the workplace and has a strong focus on primary prevention of hazards.”


Occupational Exposure Limits as defined by specific agencies:

PEL (OSHA): PEL is the maximum upper exposure legal limit to a hazardous substance that an employee can be exposed to in an 8-hour period.  A PEL is in essence the same as a TLV/REL except PELs are actual OSHA regulations which can be enforced, whereas TLV/RELs are not (unless adopted by a state OSHA). Incidentally, OSHA PELs adopted TLVs based on recommendations made by the ACGIH in 1968, meaning the existing PELs were once TLVs.  OSHA has approximately 212 chemicals with PELs.  Click on this link for information on specific OSHA PEL’s. Note OSHA website PEL links below.

TLV (ACGIH). A TLV is the “Workday Concentration” to which a worker can be exposed daily for a working lifetime without having adverse effects.  It is the averaged exposure over a workday (usually 8 hours). Another way to look at it is that TLVs are the maximum daily (8 hours) exposure to an airborne concentration of a hazardous material that healthy workers can be exposed to each workday (assuming a 40-hour workweek) without experiencing significant adverse occupational safety and health effects over a working lifetime.  ACGIH has 677 chemicals with TLVs.  TLVs are published annually in a booklet containing exposure guidelines for many commonly used substances. Click this link for more information on TLV’s at the ACGIH website.

REL (NIOSH). REL is an OEL recommended by NIOSH to OSHA to adopt as the “new” permissible exposure limit. The REL is a level that NIOSH believes would be protective of workplace safety and employee health over a working lifetime.   Although not legally enforceable, NIOSH RELs are considered by OSHA during the promulgation of legally enforceable PELs and are used as guides by some industry and advocacy organizations. NIOSH has recently added a new exposure level specific for chemical carcinogens – the RML-CA.

Furthermore, the workplace presents unique exposure possibilities. Generally, there are three subcategories: time-weighted average (TWA), ceiling value, and short-term exposure limit (STEL).

The time weighted average is measured in a workplace by sampling a worker’s breathing zone for the whole workday by using a filter media cartridge or battery which is attached to the employee.  Then, add up the total exposure and divide it by 8 hours if it was a full 8-hour test.  The result is the average exposure – the TWA.

Ceiling value is the concentration an airborne toxic substance should not exceed at any time during the workday.

STEL is the TWA (or TWA-STEL) concentration taken over a 15-minute time period (not 8 hours). For proper safety in the workplace, the set exposure level cannot be exceeded during that 15 minute test period. If a test shows that a STEL has occurred; this means that the employee has been exposed to a heavy exposure of that hazardous substance during that 15 minute test period, which is not good. You can have a recorded STEL within an 8-hour workday and still be within the TLV.  Your hazardous substance test TWA can be within the parameters.  However, if a STEL occurs within that 8-hour test period, the company will need to review the production process to see if additional controls can be applied to decrease the STEL.  If a hazardous chemical does not have a STEL (many don’t), then you rely on the TWA (8 hours).

 Additional References:

Work is dangerous to your health; a handbook of health hazards in the workplace and what you can do about them. Jeanne M. Stellman [and] Susan M. Daum. New York, Pantheon Books, 1973. ISBN 0394485254.

Occupational Safety and Health for the 21stCentury. Robert H Friis. Burlington, Massachusetts, Jones and Bartlett Learning,2016. ISBN 978128404603.




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