Benzene (71-43-2)
Benzene is a aromatic hydrocarbon with CAS Registry Number 71-43-2. 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 1 ppm. The principal target organs are the Bone marrow; blood, and workplace air is sampled and analyzed by NIOSH 1501.
Exposure Limits at a Glance
| Limit | Value | Basis |
|---|---|---|
| OSHA PEL (8-hr TWA) | 1 ppm | 29 CFR 1910.1000 |
| NIOSH REL | See note below | NIOSH Pocket Guide |
| Hazard Class | Aromatic Hydrocarbon | Aromatic |
| Target Organs | Bone marrow; blood | NIOSH / OSHA |
| Sampling Method | NIOSH 1501 | NIOSH Manual of Analytical Methods |
NIOSH REL note: NIOSH RELs are typically far more protective (e.g. benzene 1 ppm PEL vs 0.1 ppm REL). 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 Benzene is assessed against the Bone marrow; blood — the organ systems most consistently affected in occupational studies. Employers must ensure no employee’s 8-hour TWA exceeds the 1 ppm PEL, and must use engineering controls, work practices, and — where required — respiratory protection to keep exposures at or below that level.
- Hazard class: Aromatic Hydrocarbon. Aromatic-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 1501 for laboratory analysis.
- Medical surveillance: consult the OSHA substance-specific standards and the NIOSH Pocket Guide when the target organs are the Bone marrow; blood.
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 Aromatic-class agents regardless of the 8-hour average.
- Calibrate personal sampling pumps before and after each shift and record flow rates; method NIOSH 1501 specifies media, flow, and analysis.
- Compare analytical results to the OSHA PEL of 1 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 Benzene?
The OSHA Permissible Exposure Limit (8-hour TWA) for Benzene is 1 ppm.
What is the CAS number for Benzene?
The CAS Registry Number for Benzene is 71-43-2.
What are the target organs for Benzene?
The primary target organs are the Bone marrow; blood.
How do you measure Benzene in workplace air?
Use NIOSH analytical method NIOSH 1501 for air sampling and laboratory analysis.
What hazard class is Benzene?
It is classified here as a Aromatic Hydrocarbon (Aromatic).