A typical sign might look like this:

You see these signs on any building that contains hazardous chemicals. The sign is called an NFPA Panel, where NFPA stands for the National Fire Protection Association.

The idea behind these signs is to give firefighters some sort of advanced notice on what they are getting themselves into when they arrive at the scene of a fire. When there is a house fire, firefighters have a pretty good idea of what they are in for, but if there is a fire at a warehouse in an industrial park, it is very hard to know what chemicals might be stored in the warehouse. The NFPA panel is a clear indication of what sort of dangers might lie inside.

The panel has four areas, which have the following meanings:

• Red - Fire Hazard
• Blue - Health Hazard
• Yellow - Reactivity
• White - Specific Hazard
The numbers in the first 3 areas range from 0 to 4, with 0 meaning no hazard and 4 meaning severe hazard. For example, in the Reactivity area:
• 0 = Stable
• 1 = Unstable if heated
• 2 = Violent chemical
• 3 = Shock or heat may detonate
• 4 = May detonate
In the Fire Hazard Area the numbers indicate the flash point:
• 0 = Will not burn
• 1 = Above 200 degrees F
• 2 = Below 200 degrees F
• 3 = Below 100 degrees F
• 4 = Below 73 degrees F
Concrete is an example of a class 0 fire hazard. Paper and wood are class 1, and so on.

In the Health Hazard area:

• 0 = No hazard
• 1 = Slightly hazardous
• 2 = Hazardous
• 3 = Extremely hazardous