Methyl Methacrylate (MMA) is a flammable liquid used to manufacture plastics and resins. While it is regulated by OSHA and the EPA for occupational safety and toxic release reporting, it is currently NOT included on the EPA’s Risk Management Program (RMP) regulated list. It is a PSM Covered Chemical with a TQ of 10,000 pounds. MMA monomer weighs approximately 7.84 pounds per gallon; meaning that if what the FD is reporting is accurate, that single tank of 7,000 gallons would make the process a PSM covered process. (7,000 gallons X 7.84 pounds = 54,880 pounds)
Here is a breakdown of MMA’s physical and hazadous characteristics:
- RMP Exemption: MMA is not a regulated substance under the Clean Air Act Section 112(r) Risk Management Program. This means facilities housing MMA are not legally required to file a formal Risk Management Plan with the EPA, although they may still fall under general facility safety requirements.
- EPCRA & CERCLA: It is strictly tracked under other EPA frameworks. Under the Emergency Planning and Community Right-to-Know Act (EPCRA), releases meeting or exceeding a Reportable Quantity of 1,000 pounds must be immediately reported.
- Toxicity Assessment: The EPA classifies MMA as “not likely to be carcinogenic to humans,” though inhalation of its vapors causes severe neurological and respiratory irritation (e.g., chest tightness, wheezing, and dizziness).
- The Reportable Quantity (RQ) for Methyl Methacrylate (MMA) (CAS # 80-62-6) is 1,000 pounds. This RQ applies to releases into the environment within any 24-hour period under the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA).
Physical & Safety Hazards
- Flammability: MMA has a flash point of 50OF and its vapors are heavier than air. The flammable range of Methyl Methacrylate (MMA) is between 1.7% and 12.5% by volume in air. The Minimum Ignition Energy (MIE) is exceptionally low, typically ranging between 0.89 mJ and 0.97 mJ. Because this is under 1 mJ, the vapor is highly sensitive to static electricity and can be easily ignited by common electrostatic discharges (e.g., from a person or ungrounded equipment)
- The boiling point of methyl methacrylate (MMA) is approximately 214OF at standard atmospheric pressure. The vapor pressure of methyl methacrylate (MMA) is approximately 29 mmHg at 77OF (FYI… Water at 77OF is around 24 mm hg)
- Reactivity: The chemical requires the addition of inhibitors (such as hydroquinone) to prevent it from undergoing uncontrolled, exothermic polymerization. If heated or contaminated with strong acids or bases, it can build immense pressure, rupture containers, and explode.
Occupational Guidelines
- OSHA PEL: The legal airborne Permissible Exposure Limit is 100 parts per million (ppm) over an 8-hour shift.
- ACGIH TLV: The recommended Short-Term Exposure Limit is 100 ppm, with a time-weighted average of 50 ppm.
- IDLH: The Immediately Dangerous to Life or Health limit is 1,000 ppm.
- LD50: Oral exposure, the LD50 in rats ranges between 7,800 mg/kg and 10,000 mg/kg. For dermal exposure in rabbits, the LD50 is greater than 5,000 mg/kg.
- LC50: The acute inhalation LC50 in rats is officially documented at 29.8 mg/L (measured as a vapor over a 4-hour exposure period). When expressed in parts per million (ppm), various toxicological and safety sources report the 4-hour rat LC50 ranging from 5,303 ppm to 7,093 ppm depending on the specific test methodology.
Sources: SDS, NIOH, OSHA/EPA