What type of number is used to look up safety recommendations in the NAERG?

The guide number is the correct choice for looking up safety recommendations in the North American Emergency Response Guidebook (NAERG). The NAERG utilizes guide numbers to help first responders quickly access important safety information about hazardous materials. Each guide number corresponds to specific safety recommendations, emergency response actions, and information regarding the hazards associated with the materials involved in an incident.

In contrast, the other types of numbers mentioned do not serve the same purpose in the context of the NAERG. For instance, while a material identification number may refer to a specific chemical, it does not provide the immediate guidance on safety protocols that a guide number does. Similarly, a hazard identification number is used for classification of a substance's hazardous traits, while a chemical classification number categorizes chemicals based on their properties rather than offering emergency response guidance. Thus, the guide number is essential for ensuring a rapid and effective response when dealing with hazardous materials.