Imagine you get a call for a structure fire at 2am. You arrive on scene to find a commercial building with low lying, slow moving smoking that appears to be coming coming from a vent above the front door. You pull a line and force entry to find zero visibility conditions inside. Your operator radios you that he's having difficulty breathing and his skin is burning. As you acknowledge him you start to feel burning around your wrists and mask but there is no heat inside. The second engine arrives and advises you they see a diamond on the side of the building and your operator is unresponsive... What did you miss?
Let's forget about the obvious (preplan, size up etc). Was that smoke? Color and odor are two ways to distinguish smoke and vapor. Another way to tell smoke and vapor apart is by how quickly they dissipate. Most vapors dissipates rapidly, particularly if the relative humidity is low. Smoke hangs in the air, since the ash or other small particles are suspended. There are relatively few chemicals that have a vapor density less than 1, which means they rise. Most chemical vapors will sit low to the ground. Vapors tend to move slowly, unless the vapor is under pressure. Just some clues to pay attention to when you respond to a fire in a location that houses chemicals.