Time-weighted average is a worker's average exposure to a hazardous substance calculated over a standard work shift, typically 8 hours.
%20meaning.png)
A calculation method used to determine a worker's average exposure to an airborne contaminant across a full work shift, typically 8 hours, accounting for fluctuations in concentration throughout the day rather than a single point-in-time measurement.
An air monitoring device worn by a worker in a paint shop records varying solvent vapor levels throughout the shift, and the resulting TWA is compared against the substance's permissible exposure limit to confirm compliance.
TWA reflects overall exposure risk across a full shift, since brief spikes in concentration may be less significant to long-term health than sustained exposure — though short-term limits are also tracked separately for acute risks.
TWA is calculated by summing the product of each measured concentration and the time spent at that concentration, then dividing by the total sampling period, usually 8 hours.
Standard TWA calculations are based on an 8-hour shift; for extended shifts, adjusted exposure limits or modified calculation methods are often applied to account for additional exposure time.
Part of SafetyIQ's EHS glossary: plain-English definitions of workplace health and safety terms.
> Keep learning
> See it in action
Capture hazards, run inspections, track training and close out corrective actions in one platform built for high-risk, field-heavy work.
Book my free demo
Get a demo built around your sites, your teams, and the way your people work.
EHS, journey, and fatigue management software for field-heavy teams.
.png){kind=logo}
.png)