Sulfur Dioxide (7446-09-5)
Sulfur Dioxide is a acid gas / irritant with CAS Registry Number 7446-09-5. Under the OSHA air contaminants standard (29 CFR 1910.1000), its Permissible Exposure Limit (PEL) — the legal 8-hour time-weighted average (TWA) for general industry — is 5 ppm. The principal target organs are the Respiratory tract; eyes, and workplace air is sampled and analyzed by NIOSH 6004.
Exposure Limits at a Glance
| Limit | Value | Basis |
|---|---|---|
| OSHA PEL (8-hr TWA) | 5 ppm | 29 CFR 1910.1000 |
| NIOSH REL | See note below | NIOSH Pocket Guide |
| Hazard Class | Acid Gas / Irritant | Acid Gas |
| Target Organs | Respiratory tract; eyes | NIOSH / OSHA |
| Sampling Method | NIOSH 6004 | NIOSH Manual of Analytical Methods |
NIOSH REL note: NIOSH RELs often add a STEL / ceiling value to control peak irritation. The REL is a non-regulatory recommendation; where a NIOSH REL exists it is typically more protective than the OSHA PEL.
How It Enters the Body & Health Effects
Exposure to Sulfur Dioxide is assessed against the Respiratory tract; eyes — the organ systems most consistently affected in occupational studies. Employers must ensure no employee’s 8-hour TWA exceeds the 5 ppm PEL, and must use engineering controls, work practices, and — where required — respiratory protection to keep exposures at or below that level.
- Hazard class: Acid Gas / Irritant. Acid Gas-class agents are managed with the hierarchy of controls (elimination, substitution, engineering controls, administrative controls, then PPE).
- Monitoring: collect personal air samples in the breathing zone and submit them under NIOSH 6004 for laboratory analysis.
- Medical surveillance: consult the OSHA substance-specific standards and the NIOSH Pocket Guide when the target organs are the Respiratory tract; eyes.
Sampling & Compliance Notes
- Determine whether the exposure is a full-period 8-hour TWA or a short-term / ceiling scenario. Ceiling and STEL excursions apply to several Acid Gas-class agents regardless of the 8-hour average.
- Calibrate personal sampling pumps before and after each shift and record flow rates; method NIOSH 6004 specifies media, flow, and analysis.
- Compare analytical results to the OSHA PEL of 5 ppm and the NIOSH REL. Document the higher of the two for internal exposure-control targets.
- Where the PEL includes a “skin” notation, dermal absorption can contribute to the dose — glove selection and hygiene facilities are part of compliance.
Frequently Asked Questions
What is the OSHA PEL for Sulfur Dioxide?
The OSHA Permissible Exposure Limit (8-hour TWA) for Sulfur Dioxide is 5 ppm.
What is the CAS number for Sulfur Dioxide?
The CAS Registry Number for Sulfur Dioxide is 7446-09-5.
What are the target organs for Sulfur Dioxide?
The primary target organs are the Respiratory tract; eyes.
How do you measure Sulfur Dioxide in workplace air?
Use NIOSH analytical method NIOSH 6004 for air sampling and laboratory analysis.
What hazard class is Sulfur Dioxide?
It is classified here as a Acid Gas / Irritant (Acid Gas).