pool chemical signs

The photo above is of a typical sign on a door at a pool, for firefighters to know what is stored in a given space that might affect a fire or pose a danger to the firefighters.

Red means something flammable,

yellow means reactivity,

blue is a health hazard (which could include something simple like bleach)

and white is an 'other hazard', which could include environmental hazards

The numbers are on a scale of danger from 0 (zero) to four, 4 being the worst.

A couple of other symbols meaning danger include the skull and crossbones

and the corrosive chemical symbol:

A fire department hazmat expert told me that the main thing lifeguards and swim teachers should know about pool chemicals is that they should not move chemicals unless they have been trained to do so. Pool chemicals are often concentrated acids and severe burns are a big risk. He has had experience with lifeguards in swimsuits and flip flops (not a real stable platform for lifting anything) being injured.