# Hydrogen fluoride — workplace exposure limit

For Hydrogen fluoride, niosh rel (ppm) is TWA 3; niosh rel (mg/m³) is 2.5; cas no. is 7664-39-3, verified against its source on 2026-09-08.

- **Substance:** Hydrogen fluoride _(verified: appears in its own passage below)_
- **CAS No.:** 7664-39-3 _(verified: appears in its own passage below)_
- **NIOSH REL (ppm):** TWA 3 _(verified: appears in the quote below)_
- **NIOSH REL (mg/m³):** 2.5 _(verified: appears in the quote below)_

## What the source says

> NIOSH REL TWA 3 ppm (2.5 mg/m3) C 6 ppm (5 mg/m3) [15-minute]

## Where each value comes from

This source states these in separate places, so each value is shown with the passage that states it.

### Substance

> CDC - NIOSH Pocket Guide to Chemical Hazards - Hydrogen fluoride

### CAS No.

> CAS No. 7664-39-3

## Source

- https://www.cdc.gov/niosh/npg/npgd0334.html

Last verified: 2026-09-08. Review by: 2027-09-08.
Part of [US workplace chemical exposure limits: federal OSHA, Cal/OSHA and NIOSH, side by side](https://referencesource.org/workplace-exposure-limits/).