California chemical leak: What is methyl methacrylate, the chemical forcing 40,000 to evacuate?

A major chemical emergency in Garden Grove, Orange County, has forced around 40,000 residents to leave their homes after a storage tank at the GKN Aerospace facility began overheating and releasing hazardous vapours. The chemical inside the tank is methyl methacrylate, or MMA, a volatile industrial liquid used in plastics and resin manufacturing.