You've just responded to a train derailment with a fire. An unidentified number of tank cars carrying hazardous materials are reportedly involved in the incident. Initial air monitoring near the derailment using a PID and colorimetric detector tubes has confirmed the presence of organic and inorganic products of combustion and acid gases in relatively high concentrations. The Incident Commander wants the HazMat response team to conduct additional monitoring downwind of the site. Based on this information, the type of respiratory protection that should be used by the air monitoring team is