We keep hearing all these different temps from the media and OCFA. I am pretty sure they are both using Farenheit and Celsuis interchangably in their remarks and this can be confusing as heck. I just heard a media update state that “50 degrees is the happy place” for MMA. 50°F is the Flash Point of MMA and yes, below 50°F the material is BELOW its FP and thus less dangerous from its flammabiity hazard. As we know that 50°C is well above the DANGER RANGE for MMA.
So there are a number of critical temperatures we need to know regarding MMA and its ability to polymerize.
The Normal Storage Limit: 86°F
Chemical manufacturers mandate that inhibited MMA be stored BELOW 86°F. Heat naturally accelerates the slow rate at which the MEHQ inhibitor is consumed. If stored below this temperature (and properly aerated), the inhibitor will easily last its stated shelf life. If the bulk liquid temperature rises above this baseline, the inhibitor is consumed much faster, silently shortening the safe storage window.
Danger Zone: 95°F to 104°F
If the temperature of an MMA storage tank begins to rise above ambient conditions and hits this range without an external heat source, the polymerization runaway event has already begun.
This temperature rise is the physical manifestation of the inhibitor failing. The slow polymerization is generating more heat than the tank shell can dissipate to the outside air. Once this exothermic heat overcomes the cooling rate, it hits the Self-Accelerating Polymerization Temperature (SAPT), and the exponential feedback loop takes over.
Boiling Point: 212°F
If the runaway is not quenched (e.g., by dumping short-stop inhibitor chemicals into the tank), the liquid will rapidly reach 212°F. This is the boiling point of the unreacted MMA monomer.
At this temperature, the reaction is generating massive amounts of heat, and the liquid monomer is boiling violently into a flammable vapor. This is the stage where two-phase flow overwhelms the emergency relief vents, leading to a vessel rupture.
“Dead Inhibitor” Scenario
If the inhibitor is completely killed—for instance, if the tank is blanketed with 100% nitrogen, stripping the necessary oxygen—MMA can, and will, begin a runaway polymerization right at a standard room temperature of 68°F. It will just take slightly longer to reach the boiling point than if it started at a higher temperature.