Which of the following is NOT a method of determining the Guide Number as per ERG Step One?

The Guide Number in the Emergency Response Guidebook (ERG) is primarily determined through identifying the hazardous material using specific identifiers. This includes using the name of the material, referring to the four-digit ID number assigned to it, or checking placards associated with the material.

Using the volume of the material is not a method for determining the Guide Number. The Guide Number is specifically related to characteristics and risks of the hazardous materials, not their quantity or volume. The methods of determination focus on identifiers that give responders quick access to information about the material's properties and appropriate response actions.

By selecting the correct options relating to names, ID numbers, and placarding, responders can quickly find the relevant information needed for handling the situation effectively. Thus, consulting about the volume of the material does not contribute to finding the necessary Guide Number and is the correct answer to the question.