Methylene Chloride (75-09-2)
Methylene Chloride is a halogenated hydrocarbon with CAS Registry Number 75-09-2. 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 25 ppm. The principal target organs are the CNS; liver; heart, and workplace air is sampled and analyzed by NIOSH 1005.
Exposure Limits at a Glance
| Limit | Value | Basis |
|---|---|---|
| OSHA PEL (8-hr TWA) | 25 ppm | 29 CFR 1910.1000 |
| NIOSH REL | See note below | NIOSH Pocket Guide |
| Hazard Class | Halogenated Hydrocarbon | Halogenated |
| Target Organs | CNS; liver; heart | NIOSH / OSHA |
| Sampling Method | NIOSH 1005 | NIOSH Manual of Analytical Methods |
NIOSH REL note: NIOSH recommends the lowest feasible concentration (LOQ-based) for many chlorinated solvents. 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 Methylene Chloride is assessed against the CNS; liver; heart — the organ systems most consistently affected in occupational studies. Employers must ensure no employee’s 8-hour TWA exceeds the 25 ppm PEL, and must use engineering controls, work practices, and — where required — respiratory protection to keep exposures at or below that level.
- Hazard class: Halogenated Hydrocarbon. Halogenated-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 1005 for laboratory analysis.
- Medical surveillance: consult the OSHA substance-specific standards and the NIOSH Pocket Guide when the target organs are the CNS; liver; heart.
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 Halogenated-class agents regardless of the 8-hour average.
- Calibrate personal sampling pumps before and after each shift and record flow rates; method NIOSH 1005 specifies media, flow, and analysis.
- Compare analytical results to the OSHA PEL of 25 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 Methylene Chloride?
The OSHA Permissible Exposure Limit (8-hour TWA) for Methylene Chloride is 25 ppm.
What is the CAS number for Methylene Chloride?
The CAS Registry Number for Methylene Chloride is 75-09-2.
What are the target organs for Methylene Chloride?
The primary target organs are the CNS; liver; heart.
How do you measure Methylene Chloride in workplace air?
Use NIOSH analytical method NIOSH 1005 for air sampling and laboratory analysis.
What hazard class is Methylene Chloride?
It is classified here as a Halogenated Hydrocarbon (Halogenated).