Chemical Exposure Limit Calculator

No -- you must look up and enter the actual regulatory limits for your specific substance from OSHA's published PEL tables, the current ACGIH TLV booklet, or the chemical's Safety Data Sheet. These limits are set per chemical, differ by jurisdiction, and are periodically revised, so this calculator only compares the numbers you provide -- it doesn't store or assume any chemical-specific figure.

Adjusted TWA is purely a measurement calculation -- it converts your Measured Concentration and Exposure Duration into an 8-hour equivalent exposure figure. PEL, TLV, and STEL are the limits that figure gets compared against afterward, so changing them shifts whether you're over or under a limit, but never changes the measured exposure figure itself.

Short-Term Exposure Limits exist to catch brief spikes in concentration that an 8-hour time-weighted average would dilute and hide -- a short, high spike could average out to look safe over a full shift while still being hazardous during that brief window. That's why STEL Exceeded compares your raw Measured Concentration directly, not the duration-adjusted figure.

Not necessarily -- 50% of the PEL is a common industrial hygiene rule of thumb used to trigger closer monitoring before a full exceedance, but some OSHA substance-specific standards (like the lead standard) define their own action level differently, not as a flat 50% of the PEL. Check whether your specific substance has its own regulatory action level defined.

Hazard Level 2 means your Adjusted TWA over the full shift exceeds the PEL, but your instantaneous Measured Concentration hasn't crossed the typically higher STEL threshold -- meaning the exposure is a sustained-elevated-level problem rather than a brief, high-concentration spike. Both conditions call for corrective action, but they point to different exposure patterns and potentially different fixes.