Toxic warning levels, such as TLV-TWA and ERPG, are typically expressed in which unit?

Toxic warning levels like TLV-TWA (Threshold Limit Value-Time Weighted Average) and ERPG (Emergency Response Planning Guidelines) are generally expressed in parts per million (ppm). This unit is commonly used in environmental health and safety to represent the concentration of a substance within a given volume of air or water.

Using ppm allows for easier comprehension when dealing with trace levels of toxic substances, as it indicates how many parts of the toxic substance are present per million parts of the air or liquid. This makes it a practical choice for assessing potential health risks in various settings, such as workplaces or during emergency situations, where understanding the ambient concentration of hazardous materials is crucial for safety evaluations and response strategies.

While other units such as milligrams per liter or parts per trillion may also be used in specific contexts, they do not typically apply to the standard expressions of TLV-TWA or ERPG values, which are widely recognized in regulatory and safety framework discussions.