NFPA 1991 specifies minimum requirements for design, performance, testing, and certification of elements of vapor-protective ensembles for emergency responders to hazardous materials incidents, and chemical or biological terrorism incidents, for protection from specified chemical vapor, liquid splash, and particulate exposures. The Standard also provides additional optional requirements for protection from chemical and biological agents that could be released during a terrorism incident, chemical flash fire protection, liquefied gas protection, and combined chemical flash fire and liquefied gas protection.