It is a DOT hazardous materials placard indicating compressed oxygen.
The placard on a tanker carrying hazardous materials will tell you the class of the hazard (flammable, explosive, corrosive, etc). If you have access to the North American Guide or a similar reference, the placard will also tell you something a bit more specific about the identity of the hazardous material - its category, or sometimes its chemical name.
The hazard class of the substance being carried
Shipment contains a mixed load of hazardous materials
Hazardous materials identified in vehicles and rail cars through the use of placards.
The DOT hazardous materials placard for organic peroxides may be - an all-yellow diamond shape with "ORGANIC PEROXIDE" and "5.2" lettering, or - the revised DOT placard which is red on top and yellow on the bottom, with a stylized flame in the red area.
Placards are not used in maritime shipping of hazardous materials. Even in US ground transportation, placards are not required for the shipment of "Limited Quantities."
4 sides require placards. Front, back, and both left/right sides.
The DOT placard for organic peroxides is a yellow diamond with "ORGANIC PEROXIDE" lettering and the hazard identifying number "5.2" on it. The revised international version is red on top, yellow on the bottom, with a stylized flame symbol in the red and the numbers 5.2 in the yellow.
In the scheme used for transport of hazardous materials there are eight (8) classes of hazardous materials.
When analyzing a hazardous materials incident at the awareness level you are responsible for recognizing the presence of hazardous materials.
Whether planned procedures workThe purpose of conducting a hazardous materials exercise is to practice your response to a hazardous materials event without having to deal with "real" hazardous materials. This is the equivalent in hazardous materials of maneuvers or war games in the military, or of fire drills in school.