GKN AEROSPACE — HAZARD ZONE SIMULATOR

The explosion radius, up close

What to expect at each distance from the tank. These rings track the current scenario in the simulator, so they grow and shrink as you change the leak rate, cascade tanks, and yield.

The mechanism most coverage misses

MMA (methyl methacrylate) is a monomer: a liquid that wants to link up into plastic. It is kept stable by a small amount of inhibitor. If the tank loses that inhibitor or heats up, the MMA begins to polymerize, turning into solid acrylic, the same material as Plexiglas. That reaction gives off heat, and the heat makes it run faster, so it can accelerate on its own. A tank that stays in crisis for days is a slow polymerization runaway that crews are working to keep cool.

It is a race between two endings

• Controlled: the heat escapes fast enough and the contents harden into a block of solid plastic. The tank is destroyed, but there is no explosion. Keeping it cool is what produces this outcome.
• Runaway: heat builds faster than it can escape. The remaining liquid boils (MMA boils near 100°C / 212°F) and flashes to vapor, pressure climbs, and the tank ruptures. At very high temperature the new plastic can break back down into vapor, adding still more pressure.

So it solidifies and pressurizes at the same time. Which one finishes first decides whether you get a ruined tank or an explosion.

Three ways a failure can go

• BLEVE (boiling-liquid expanding-vapor explosion): the tank bursts while its contents are superheated. Fireball, pressure blast, and tank fragments thrown far.
• Vapor-cloud explosion: vapor that has pooled along the ground drifts out, finds an ignition source, and ignites all at once. This is what the simulator's blast rings estimate.
• Pool fire: the spilled liquid simply burns, feeding the toxic plume.

Why the zones look the way they do

The blast rings run from the fireball out to a glass-break radius. That outer ring matters most for injuries: windows shatter blocks away and flying glass hurts people who felt safe. The toxic plume is separate. MMA vapor is heavier than air, so it hugs the ground and drifts downwind, irritating eyes and lungs. The evacuation area is sized for the glass-break radius plus the downwind plume, which is why the wind direction changes the picture so much.