Which placard would NOT be used for flammable substances?

The correct answer identifies that Guide 153 would not be used for flammable substances. Each guide in the Emergency Response Guidebook is assigned a specific type of hazardous material it corresponds to.

Guide 153 pertains to "Carbon Dioxide" and is specifically related to non-flammable gas and not classified under flammable substances. This makes it unsuitable for use with materials that are flammable or pose a fire hazard.

In contrast, other guides like 127, which addresses flammable liquid materials, and 111 and 154, which cover various types of flammable or combustible substances, are indeed applicable for the identification and handling of flammable materials. Thus, Guide 153 distinctly stands out as the correct choice in this context, as it pertains to a substance that does not fall under the flammable category.