An established set of procedures is followed to investigate the site, evaluate the threat, and determine the best course of action. First, EPA designates an On-Scene Coordinator (OSC) to evaluate the incident and determine the appropriate response agency. If the OSC determines that EPA will take the lead in responding to the incident, the OSC will evaluate the urgency of the situation to determine the appropriate response alternative.

Once the type of response alternative is determined, response personnel take special precautions to ensure that they are protected from the threats posed at the site. When entering the site, response personnel wear personal protective gear to shield them from the chemical, physical, and biological hazards. The selection of the type of personal protective equipment is based on:

• the identification of the hazards or suspected hazards,
• potential exposure pathways, and
• the performance of the equipment in providing a barrier to these hazards.

As response personnel enter the site, they further evaluate the site risks and hazards present. Generally, response workers will conduct a visual survey and may perform air monitoring for potential dangers. Direct-reading instruments and testing equipment are used when performing air monitoring. One important goal of monitoring during initial site entry is to establish safety zones at the site. Periodic monitoring is then conducted to ensure that any new hazards are identified promptly, and that appropriate controls are implemented to protect the responders and nearby communities.