NFPA 704 placards are divided into four colored quadrants, or four "mini" diamonds within the larger diamond ... hydrocyanic acid (hydrogen cyanide), hydrogen sulfide, phenol, phosphine ...

One such sign is NFPA 704 – perhaps better known as the “fire diamond.” An NFPA 704 sign out in the wild. According to the sign, whatever is behind that door is very, very dangerous and ...