# Tin(II) oxide (as Sn) — workplace exposure limit

For Tin(II) oxide (as Sn), niosh rel (mg/m³) is TWA 2; cas no. is 21651-19-4, verified against its source on 2026-09-08.

- **Substance:** Tin(II) oxide (as Sn) _(verified: appears in its own passage below)_
- **CAS No.:** 21651-19-4 _(verified: appears in its own passage below)_
- **NIOSH REL (mg/m³):** TWA 2 _(verified: appears in the quote below)_
- **PEL (mg/m³):** 2 _(per dir.ca.gov, not stated by the source above)_

## What the source says

> NIOSH REL TWA 2 mg/m3

## 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 - Tin(II) oxide (as Sn)

### CAS No.

> CAS No. 21651-19-4

## What dir.ca.gov says

> 21651194 | | Tin, tin oxide and inorganic compounds, except SnH $4, as Sn | -- | 2

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

## Source

- https://www.cdc.gov/niosh/npg/npgd0615.html
- 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/).