There are seven major clues for detecting the presence of hazardous materials. The relative risk to a person increases as the number increases:

  1. Occupancy/location
  2. Container shapes
  3. Markings and colors
  4. Placards and labels
  5. Shipping papers
  6. Detection devices
  7. Your senses

(lowest risk)

(medium risk)

(highest risk)


The National Fire Protection Association (NFPA) System for Marking of Buildings

The NFPA has developed a marking system for fixed facilities known as the Fire Diamond. It is divided into four sections, each section is assigned a color which indicates a specific type of hazard. The four sections and the colors associated with each are:

Blue - Health

Red - Flammability

Yellow - Reactive

White - Special information

Fire Diamond

Each colored section is marked numerically to include order of severity of hazard, the high the number, the greater the hazard.
Fire Hazard - Red
4 Flash Point below 73 F (Boiling Point below 100 F)
3 Flash Point below 73 F (Boiling point at/above 100 f) and/or at/above 73 F
- not exceeding 100 F
2 Flash Point above 100 F, not exceeding 200 F
1 Flash Point above 200 F
0 Will not burn

Reactivity (Instability) - Yellow
4 May detonate
3 Shock and heat may detonate
2 Violent chemical change
1 Unstable if heated
0 Stable

4 Deadly
3 Extreme Danger
2 Hazardous
1 Slightly Hazardous
0 Normal Material

Specific Hazard - White
OX or OXY Oxidizer
W (with line through it) Use no water

Department of Transportation (DOT) Placards and Labels

DOT placards are diamond shaped, 10 3/4" square. They are used on vehicles in transit. DOT labels are 4" X 4" square and are intended for use on small packages. They provide information four ways:

  1. Color
  2. Numbers
  3. Symbols       Link to DOT Placards
  4. Words


Red & White
Black & White
Yellow & White

Flammable Liquids or Gas
Flammable Solid
Oxidizer/Organic Peroxide
Water Reactive
Non-Flammable Gas


UN and NA Numbers

A four digit ID number called a UN (United Nations) or NA number is sometimes located across the center of a DOT placard. This number is also required to appear on the DOT shipping papers. A list of these numbers and their corresponding chemicals can be found in the DOT Guide Book.

United Nations Hazard Class or Division Numbers are found in the lower corner of a DOT placard. Labels are not required to have the UN number on them. These numbers serve to specifically identify the hazardous material in the DOT Emergency Response Guidebook.

The nine United Nations Classes are:

Class 1 Explosives

Division 1.1 - Mass explosion hazard
Division 1.2 - Projection hazard
Division 1.3 - Predominantly a fire hazard
Division 1.4 - No significant blast hazard
Division 1.5 - Very insensitive explosives

Class 2 Gases

Division 2.1 - Flammable gases
Division 2.2 - Nonflammable gases
Division 2.3 - Poison gases
Division 2.4 - Corrosive gases (Canadian)

Class 3 Flammable liquids

Division 3.1 - Flashpoint below -18C (0 degrees F)
Division 3.2 - Flashpoint -18C to 23C (73F)
Division 3.3 - Flashpoint 23C to 61C (141F)

Class 4 Flammable Solids

Division 4.1 - Flammable solids
Division 4.2 - Spontaneously combustible
Division 4.3 - Dangerous when wet

Class 5 Oxidizers/Organic Peroxides

Division 5.1 - Oxidizers
Division 5.2 - Organic peroxides

Class 6 Poisons

Division 6.1 - Poisonous material
Division 6.2 - Etiologic materials

Class 7 Radioactive

Class 8 Corrosives

Class 9 Miscellaneous