The level of concentration below which no adverse effects are expected to occur is referred to as:

The term that defines the level of concentration below which no adverse effects are expected to occur is known as the Permissible Exposure Limit (PEL). PELs are established by regulatory organizations, such as the Occupational Safety and Health Administration (OSHA), to ensure worker safety by limiting exposure to hazardous substances in the workplace.

PEL is legally enforceable and is an important aspect of safety standards in various industries, particularly those that deal with toxic or hazardous materials. By adhering to these limits, employers can create a safer environment for their employees and reduce the risk of health issues related to exposure.

The other terms, while related to exposure limits, do not specifically define this threshold. An Action Level is typically a specific concentration that triggers the need for further controls or monitoring, but it does not necessarily indicate a level where no adverse effects occur. TLV (Threshold Limit Value) refers to levels recommended by the American Conference of Governmental and Industrial Hygienists (ACGIH) for occupational exposure but may not have the same enforceability as PELs. A Ceiling Limit is a concentration that should never be exceeded during any part of the workday but does not provide a threshold for no adverse effects in the same way PELs do.