# Ethylene oxide — workplace exposure limit

For Ethylene oxide, niosh rel (ppm) is C 5; niosh rel (mg/m³) is 9; cas no. is 75-21-8, verified against its source on 2026-09-08.

- **Substance:** Ethylene oxide _(verified: appears in its own passage below)_
- **CAS No.:** 75-21-8 _(verified: appears in its own passage below)_
- **NIOSH REL (ppm):** C 5 _(verified: appears in the quote below)_
- **NIOSH REL (mg/m³):** 9 _(verified: appears in the quote below)_
- **PEL (ppm):** 1 _(per dir.ca.gov, not stated by the source above)_
- **PEL (mg/m³):** 2 _(per dir.ca.gov, not stated by the source above)_
- **STEL (ppm):** 5 _(per dir.ca.gov, not stated by the source above)_

## What the source says

> NIOSH REL Ca TWA <0.1 ppm (0.18 mg/m3) C 5 ppm (9 mg/m3) [10-min/day]

## 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 - Ethylene oxide

### CAS No.

> CAS No. 75-21-8

## What osha.gov says

> Ethylene oxide; see 1910.1047 | 75-21-8 | - | - | - |

Source: https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1000TableZ1

## What dir.ca.gov says

> 75218 | | Ethylene oxide; see Section 5220 | 1 | 2 | | 5

Source: https://www.dir.ca.gov/title8/5155.html

## Source

- https://www.cdc.gov/niosh/npg/npgd0275.html
- https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1000TableZ1
- https://www.dir.ca.gov/title8/5155.html

Last verified: 2026-09-08. Review by: 2027-08-05.
Part of [US workplace chemical exposure limits: federal OSHA, Cal/OSHA and NIOSH, side by side](https://referencesource.org/workplace-exposure-limits/).