What this section is about
This section groups calculation tools useful for industrial hygiene practice in Quebec and elsewhere. Specialized unit conversions, time-weighted averages, ventilation, noise, heat stress, exposure statistics. Each tool applies a recognized formula. Sources are cited at the bottom of every tool.
We do not pre-fill regulatory values (OELs, TLVs, PELs) — you enter the value applicable to your situation, which avoids licensing issues and ensures you work with the current version of the relevant reference. Everything runs in your browser; no data is sent to any server.
These calculators do the math. They don't do the thinking. Use them to check a number, sketch a scenario, or sanity-test a vendor claim — but the call about whether your workplace is actually safe still belongs to a certified industrial hygienist who knows the substance, the worker, and the room.
Conversions and units
- ppm ↔ mg/m³ Converter — Convert atmospheric contaminants between ppm and mg/m³ at any T and P.
- Industrial Hygiene Units Converter — Pressure, flow, velocity, and aerosol concentrations — beyond a generic unit converter.
Exposure assessment
- TWA Calculator — Time-weighted average exposure across multiple samples.
- STEL / Excursion Checker — Verify peaks against STEL or the ACGIH 3× / 5× excursion rule.
Industrial ventilation
- Flow Rate Calculator (Q = V × A) — Volumetric airflow from velocity and section. Round, rectangular, or direct area.
- Air Changes per Hour (ACH) — Room ventilation rate, or required airflow for a target ACH.
- Velocity Pressure ↔ Air Velocity — Pitot-tube physics with optional density correction.
Noise
- Noise Level Addition — Combine multiple sound sources logarithmically.
- Noise Distance Attenuation — Sound level vs distance for point or line sources in free field.
- Noise Dose & TWA — Cumulative dose using NIOSH, OSHA, or Quebec criteria.
- Hearing Protector Effectiveness (NRR) — Effective NRR via the CCOHS / CSA Z94.2 derating method.
Physical agents
- WBGT Calculator (Heat Stress) — Wet-bulb globe temperature for indoor or outdoor environments.
- Inverse Square Law — Intensity vs distance for point-source radiation in free space.