FAQs on OCCUPATIONAL LIMITS
When to use SHORT TERM EXPOSURE LIMITS ?
a.Fluctuating exposure levels: If workers are exposed to rapidly changing concentrations of a hazardous substance, STEL limits can help ensure that short-term peaks in exposure do not pose significant risks to workers' health.
b. Task-based exposure: When workers perform tasks that involve brief but intense exposure to hazardous substances, such as maintenance, cleaning, or the handling of concentrated chemicals, STEL limits can help protect workers from acute health effects.
c. Acute health effects: For substances that can cause acute or immediate health effects, such as irritation, dizziness, headaches, or respiratory distress, STEL limits provide guidance for managing short-term exposures.
d. Supplementing TWA limits: STEL limits are often used in conjunction with Time-Weighted Average (TWA) limits, which represent average exposure over a longer period (usually an 8-hour workday). While TWA limits help protect workers from long-term or chronic health effects, STEL limits help address the risks associated with short-term, high-concentration exposures.
2. Can I use IDLH (Immediately Dangerous to Life or Health)
a. you should not take IDLH (Immediately Dangerous to Life or Health) values as the exposure limit in most workplace situations. IDLH values represent concentrations of hazardous substances that pose an immediate threat to life, would cause irreversible adverse health effects, or impair an individual's ability to escape from a dangerous environment. They are generally used for emergency response purposes and are not intended as regular exposure limits for the workplace.
3. What does TWA: x ppm skin means ?
a.The sign "TWA: x ppm Skin" refers to an exposure limit standard for a specific chemical or substance in the workplace. It contains two parts: TWA and Skin notation.
b. TWA (Time-Weighted Average): TWA is an average concentration of a chemical in the air that a worker is exposed to over a specific period, usually an 8-hour workday. In this case, the TWA limit is set at 5 parts per million (ppm), which means that, on average, a worker should not be exposed to a concentration higher than 5 ppm of the substance in the air during an 8-hour work shift. This limit is designed to protect workers from potential health hazards associated with long-term exposure to the chemical.
c. Skin notation: The "Skin" notation indicates that the substance can be absorbed through the skin, mucous membranes, or eyes, and can contribute to the overall exposure. This notation serves as a warning that protective measures should be taken to prevent skin contact with the substance, as skin absorption can lead to systemic toxicity or other health effects.
4. What is the meaning of the term Vacated PEL means ?
a. The term "OSHA vacated PEL" refers to Permissible Exposure Limits (PELs) that were established by the Occupational Safety and Health Administration (OSHA) but were later vacated or invalidated by a court ruling. PELs are regulatory limits on the concentration of a substance or agent in the air, intended to protect workers from adverse health effects due to occupational exposure.
b. In 1989, OSHA issued a comprehensive revision of its PELs for various substances in the workplace. However, in 1992, a U.S. appeals court (in the case AFL-CIO v. OSHA) vacated or invalidated many of the new PELs, ruling that OSHA had not provided adequate justification for the revised limits.
c. As a result of this ruling, OSHA reverted to the previous PELs established in 1970, based on the 1968 Threshold Limit Values (TLVs) by the American Conference of Governmental Industrial Hygienists (ACGIH). The term "OSHA vacated PEL" is often used to refer to the 1989 PELs that were invalidated by the court ruling, and are no longer legally enforceable.
d. It is important to note that even though the vacated PELs are not legally enforceable, they may still provide useful information on the potential hazards associated with exposure to certain substances. Employers and industrial hygienists should also consider other sources of occupational exposure guidelines, such as the ACGIH TLVs or the NIOSH Recommended Exposure Limits (RELs), which may be more up-to-date and based on more recent scientific evidence
5. Can I use STEL and PEL at the same time during an exposure assessment ?
a. Yes, using STEL (Short-Term Exposure Limit) and PEL (Permissible Exposure Limit) together can provide comprehensive protection for workers exposed to hazardous substances. These two types of exposure limits serve different purposes and complement each other in managing the risks associated with both short-term and long-term exposures.
b. PEL (Permissible Exposure Limit): PELs are regulatory limits set by OSHA, representing the maximum allowable concentration of a hazardous substance in the air averaged over an 8-hour workday (time-weighted average or TWA). PELs are designed to protect workers from chronic health effects that may result from prolonged exposure to a substance. Employers are legally required to ensure that workers' exposure to hazardous substances does not exceed the established PELs.
c. STEL (Short-Term Exposure Limit): STELs are exposure limits that represent the maximum concentration of a substance workers can be exposed to over a short period, typically 15 minutes. STELs help protect workers from acute health effects or irritation that may result from brief but intense exposures to hazardous substances. While not all substances have a designated STEL, they are an essential part of exposure management when dealing with substances that pose short-term risks.
d. Using PEL and STEL together allows employers and industrial hygienists to manage both long-term and short-term exposures, ensuring that workers are protected from the full range of potential health effects associated with hazardous substances. To accomplish this, it is crucial to monitor the workplace environment, implement appropriate engineering controls, and provide personal protective equipment (PPE) when necessary. Additionally, worker education and training are vital for understanding and adhering to these exposure limits.