Remember the threat levels moving from green to yellow which basically provided no information about what to actually do? Apparently it's just as bad inside the TSA. Some are worried about a Thermite threat on plane which would be difficult to put out and potentially deadly. There's not specific threat and it would be difficult to get a device and igniter past screening but it's still a threat. So what should be done if such a device goes off on board? Well they just tell you what not to do.
The Intercept reports TSA Issues Secret Warning on ‘Catastrophic’ Threat to Aviation "TSA warned federal air marshals not to use customary methods of extinguishing fires — the water or halon fire extinguishers currently found on most aircraft — which would make the reaction worse, creating toxic fumes. Instead, air marshals are told to ‘recognize a thermite ignition’ — but TSA has provided no training or guidance on how to do so, according to multiple sources familiar with the Issue."