What are the two main types of exposure limits?

The correct choice highlights the two primary categories of exposure limits that are used to assess and manage worker safety in environments where hazardous substances are present. Short-term exposure limits (STELs) are designed to protect workers from short-term, acute effects of exposure to harmful agents, typically over a short duration, such as 15 minutes. These limits help to ensure that any peak exposures do not exceed safe levels, thus minimizing the risk of immediate harmful effects.

Time-weighted averages (TWAs) provide a broader perspective on exposure by averaging the concentration of a substance in the air over an extended period, usually an 8-hour work shift. This measure accounts for variations in exposure throughout the working day and is crucial for understanding long-term health impacts. Together, STELs and TWAs create a comprehensive framework for protecting workers from both short-term and long-term effects of hazardous substance exposure, making this combination essential for an effective occupational health strategy.