Chemical Exposure in Industrial Facilities

Many agencies are responsible for oversight of working condition safety in dangerous environments, including as the Occupational Safety and Health Administration (OSHA), the National Institute for Occupational Safety and Health (NIOSH) and the American Conference of Governmental Industrial Hygienists (ACGIH). These organizations have developed standards to measure the level of airborne toxic substances that a manufacturing facility may expose its workers. These standards measure substances in parts per million (ppm) for gases and milligrams per cubic meter (mg/m3) for particulates.

The Recommended Exposure Levels (REL) are recommendations from NIOSH to OSHA regarding the exposure of workers to certain substances. In turn, OSHA considers these recommendations when creating federal standards for worker safety. Industry groups and safety advocacy watchdogs also use RELs as guidelines for how facilities should operate to protect their workers. According to NIOSH standards, the REL is a level that takes into account employee safety during their tenure at a facility, along with protective equipment such as goggles and masks, prominent signs warning of potential dangers, monitoring of exposure levels, and other prudent safety measures. Typically, concentration levels that comply with REL standards are not considered to be injurious to workers.

The Threshold Limit Value (TLV) is similar to the REL and is made up of recommendations from ACGIH to OSHA. However, where RELs relate to day-to-day exposure to substances, the TLV deals with chronic exposure and the effects such exposure can have on a worker's long-term health. Many of the current limits set by OSHA were based on these recommendations.

The Permissible Exposure Limit, referred to in the industry as PEL or OSHA PEL, is a restriction backed by federal law for vulnerability of an industrial worker to any chemical, substance or background element such as noise, vibration, heat or ionization. The federal agency known as the Occupational Safety and Health Administration (OSHA) establishes these Permissible Exposure Limits and enforces them with federal inspectors. Facilities that exceed these limits may face fines and suspension of operations until their plants are brought into compliance.

Each of these agencies sets their limits in three ways:

• The Short-Term Exposure Limit (STEL) considers the level of exposure during a short period during a work shift (e.g. fifteen to thirty minutes). For substances that can damage tissue or cause debilitating pain quickly, industrial safety personnel monitor this level closely.
• The Time-Weighted Average (TWA) is a measure of the level of exposure during either an eight-hour workday or a forty-hour workweek. This entails that, for fixed time periods, an employee possibly could be exposed at higher levels than recommended the PEL, as long as the average concentration over the course of the work day stays under the TWA.
• The Ceiling Limit is a limit that cannot be exceeded or worker safety is considered to be in imminent danger.

Below is an example of an OSHA report all agencies’ reports on exposure limits to ozone (O3, also called Triatomic Oxygen).

Ozone:
OSHA Permissible Exposure Limit (PEL) for General Industry: 29 CFR 1910.1000 Z-1 Table -- 0.1 ppm, 0.2 mg/m3 TWA
OSHA Permissible Exposure Limit (PEL) for Construction Industry: 29 CFR 1926.55 Appendix A -- 0.1 ppm, 0.2 mg/m3 TWA
OSHA Permissible Exposure Limit (PEL) for Maritime: 29 CFR 1915.1000 Table Z-Shipyards -- 0.1 ppm, 0.2 mg/m3 TWA

American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV): Heavy Work - 0.05 ppm TWA; Moderate Work - 0.08 ppm TWA; Light Work - 0.10 ppm TWA; Heavy, Moderate, or light workloads (<= 2 hrs) - 0.20 TWA; Appendix A4 - Not Classifiable as a Human Carcinogen

National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL): 0.1 ppm, 0.2 mg/m3 Ceiling