REL and ERPG are exposure limits used in toxic release assessment. Which of the following best describes their purpose?

• A. They define ignition energy.
• B. They define boiling points.
• C. They measure wind speed.
• D. They provide health-based exposure limits to compare predicted concentrations against.

Answer: (D)

In toxic release assessment, you interpret how much of a chemical people might breathe by comparing predicted air concentrations to health-based thresholds. REL and ERPG are such thresholds—they set concentration values that reflect potential health effects, rather than physical properties like ignition energy or boiling points. You use these limits to judge risk: if the predicted concentration is below these thresholds, exposures are considered acceptable from a health perspective; if it approaches or exceeds ERPG levels, it signals progressively stronger protective actions, and REL-type limits help gauge safe occupational exposure. That’s why they’re described as health-based exposure limits to compare predicted concentrations against.