INTRODUCTION TO OCCUPATIONAL HEALTH

Ceiling (TLV-C)

Ceiling (TLV-C) is the concentration that should not be exceeded even instantaneously. Although the time-weighted average concentration provides the most satisfactory and practical way of monitoring airborne agents for compliance with the limits, there are certain substances for which it is inappropriate. In the latter group are substances which are predominantly fast acting and whose threshold limit is more appropriately based on this particular response. Substances with this type of response are best controlled by a ceiling "C" limit that should not be exceeded.

For some substances, for example irritant gases, only the TLV-ceiling may be relevant. For other substances, either two or three categories may be relevant, depending upon their physiologic action.