 More recently MIC was involved in an explosion at a pesticide manufacturing plant in West Virginia.Exposure limits can be expressed as ceiling limits, a maximal value, short-term exposure limits (STEL), a 15-minute exposure limit or an 8-hour time-weighted average limit (TWA).Below is a sampling, not exhaustive, as less common isocyanates also have specific limits within the United States, and in some regions there are limits on total isocyanate, which recognizes some of the uncertainty regarding the safety of mixtures of chemicals as compared to pure chemical exposures.