Safety Symbols for Chemical Hazards

Written by krista niece
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Safety Symbols for Chemical Hazards
This DOT placard warns emergency personnel that the chemical inside is in Class 5, Division 1. (oxidiser class 5.1 placard image by k9dg from

Chemical safety hazards can show up in surprising places--on the road, in farmland or at your local grocery store. Federal regulations require chemical hazards to be identified by special signs, but often the meaning of these signs are not immediately apparent. Keep your eyes open as you go about your day, and have fun "sign-spotting."

The NFPA "Fire Diamond"

The National Fire Protection Agency (NFPA) is a private, non-profit organisation that makes recommendations on fire prevention policies. NFPA Code 704 defines the well-known "fire diamond" that gives a concise, easy-to-read summary of a chemical's dangerous properties. Clockwise from the top, the four quadrants of the diamond give a numerical (1-4) ranking of the chemical's flammability (red), reactivity (yellow), special hazards (white), and health hazards (blue). Many facilities follow the NFPA's recommendation that every chemical on the premises be appropriately labelled with a fire diamond. Often there is also a fire diamond near the door to a facility that houses chemicals, such as a warehouse or store. The NFPA states on its website that the information in the fire diamond is primarily for use by emergency personnel and is "not applicable to chronic exposures or to nonemergency occupational exposure."

DOT Placards

These Department of Transportation (DOT)-required signs are visible on every chemical shipment travelling by land, sea or air. DOT placards are diamond-shaped and have four features that provide information about the shipment: (1) on the lower half of the diamond, a class number (1-9) or the designation "ORM" for "other regulated materials" to designate the nature of the chemical's primary hazard (1=explosive, 2=gas, 3=flammable liquid, etc.); (2) in the centre of the diamond, a four-digit number specific to the chemical being transported or a general warning that corresponds to the class number (e.g., 'CORROSIVE'); (3) often, a graphic in the top half of the diamond (stylised flames for flammability, skull and crossbones for toxicity) reiterates the danger or provides additional information; (4) distinctive background colours or patterns allow rapid sign recognition from a distance. Like the fire diamond, DOT placards are primarily intended for use by emergency personnel, for instance in the case of an overturned vehicle. The authoritative document for interpreting DOT placards is the Emergency Response Guidebook (ERG) published by the U.S. Department of Transportation.

Safety Symbols for Chemical Hazards
This Class 4 substance is DANGEROUS WHEN WET, indicated in words and by the blue background. The stylised flames indicate fire danger on contact with water. (Dangerous when wet placard image by k9dg from

OSHA Signs

The Occupational Safety and Health Administration (OSHA) has implemented general guidelines on sign design for chemical safety as well as other purposes. Unlike NFPA and DOT signs, which are highly standardised and intended for emergency use, OSHA signs can be customised and are primarily for use by workers. As stated on the OSHA website, OSHA sign design guidelines are "intended to cover all safety signs except those designed for streets, highways, railroads, and marine regulations," making these signs very common in the workplace, including chemical environments. OSHA signs are rectangular with rounded edges. The top half of the sign bears one of several standardised messages, which in descending order of urgency are DANGER, WARNING, CAUTION, NOTICE and SAFETY FIRST. The signs are colour-coded for easy recognition and the bottom half of each sign contains a customised message alerting the reader to the specific conditions that are present.

ANSI Signs

The American National Standards Institute (ANSI), like NFPA, is a private, non-profit organisation composed of experts but carrying no legislative weight. ANSI Standard Z535 contains guidelines on designing safety signs, including chemical hazard signs. Design principles under ANSI include the use of 'action phrases' that tell the reader how to avoid the hazard (e.g., 'Wear a Respirator'), listing of possible consequences if the hazard is not respected, bold headers and illustrations to attract notice and contact information in case of an emergency. Some of these ANSI guidelines have been incorporated into OSHA regulations, giving them the force of law.

Safety Symbols for Chemical Hazards
This 'laser-danger' sign incorporates several ANSI design principles. (danger image by Wolszczak from

A Final Note on Safety Signs

It's fun and informative to be able to look at the truck in front of you in the traffic jam and know what kind of chemical it's carrying. But if you are in a situation where your safety depends on correct interpretation of a chemical hazard sign, consult a safety expert familiar with your location and circumstances. This article is intended for informational purposes only.

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