What characteristic of a substance prompts the need for special response measures as indicated in the ERG?

The need for special response measures as indicated in the Emergency Response Guidebook (ERG) is primarily prompted by substances that are classified as explosives, toxic, or reactive. These classifications indicate that the substance poses significant hazards to health and safety, environmental integrity, or property.

Explosive substances require careful handling and specific protocols to prevent detonation, which can cause widespread damage and casualties. Toxic substances can pose serious health risks, leading to injury or death if inhaled, ingested, or absorbed through the skin. Reactive substances can undergo uncontrolled chemical reactions, which can result in fires, explosions, or the release of harmful gases, posing further threats during an emergency.

The ERG is designed to guide responders in identifying these dangers and implementing appropriate safety measures to mitigate risks associated with these hazardous materials, thereby ensuring a safer response to incidents involving such substances. The other characteristics listed do not inherently indicate a need for special measures, as they do not directly relate to the potential dangers posed by the materials involved.