Here is where experience, judgement and professional knowledge kicks in. Selection must be based on an evaluation of the performance characteristics of the protective clothing relative to the requirements and limitations at the incident scene, the task-specific conditions to be encountered by responders, and the hazards and potential hazards identified at the incident site.
When intentional, criminal release of chemical/biological agents is involved, ensembles manufactured and independently certified to NFPA 1994, Protective Ensembles for Chemical/Biological Terrorism Incidents, should be used. The NFPA 1994 standard addresses three levels of protective ensembles that may be selected based on performance requirements. (Note that the requirements stated in NFPA 1994 are based on a single exposure wearing of the protective ensemble for such chemical/biological terrorism incidents. The ensemble consists of garments, gloves and footwear approved as a system.)