Chemical Classification & Safety Signs

The National Fire Protection Association - NFPA uses a symbol system designed as a diamond-shaped label containing four differently colored squares. A number (0 - 4) or an abbreviation is added to each square indicating the order of hazard severity. The higher the number, the greater the hazard.

Red Background
  • 4 - flash point < 73 oF
  • 3 - flash point < 100 oF
  • 2 - flash point
    > 100 oF < 200 oF
  • 1 - flash point > 200 oF
  • 0 - will not burn

Yellow Background
  • 4 - explosive at room temp
  • 3 - shock and heat may detonate
  • 2 - violent reaction with water
  • 1 - unstable if heated, not violent
  • 0 - not reactive with water
NFPA symbol
Blue Background
Health Hazard
  • 4 - deadly
  • 3 - extreme danger
  • 2 - hazardous
  • 1 - slightly hazardous
  • 0 - normal material

White Background
Specific Hazard
  • oxidizer OX
  • acid ACID
  • alkali ALK
  • corrosive CORR
  • use NO WATER

Flammable Materials:
  • Flammability is a measure of how easily a gas, liquid, or solid will ignite and how quickly the flame, once started, will spread. Flammable liquids themselves are not flammable; rather, the vapor from the liquids are combustible.
  • The flash point of a material is the temperature at which a liquid (or volatile solid) gives off vapor in quantities significant enough to form an ignitable mixture with air. Given an external source of ignition (i.e., spark, flame), a material can ignite at temperatures at or above its flash point.
  • Pyrophoric materials can ignite spontaneously with no external source of ignition. For instance, the Group 1 metals on the periodic table react with water to produce hydrogen and heat. Often this heat is enough to ignite the hydrogen.
  • Examples of commonly-used flammable chemicals:
    • acetone
    • hydrogen
    • ethyl ether
    • sodium
    • ethyl alcohol
    • acetylene
Health Hazard
  • A carcinogen is an agent capable of causing cancer, as designated by the Occupational Safety and Health Administration (OSHA). Long-term exposure to carcinogenic substances can result in cancers of various types. A number of substances have been found to be capable of producing cancer following exposure by inhalation, ingestion, or skin contact.
  • Known carcinogens should not be used by students in our high school lab.
  • The following terms are used to describe carcinogenic materials:
    • Sufficient positive -- Those chemicals that were found to promote and increase incidence of malignant tumor in a multiple species or strain of lab animals.
    • Limited positive -- Those chemicals found to promote either malignant tumors in a single strain, or benign tumors in single or multiple species or strain.
    • Inadequate -- Insufficient evidence to make a decision.
    • Equivocal -- Almost no supporting evidence.
    • Negative -- (limited or sufficient) significant negative evidence.
  • Examples of known or suspected high risk carcinogens:
    * Designates an EPA controlled substance.
    • 4-Nitrobiphenyl
    • Methylchloromethyl ether
    • 3,3'-Dichlorobenzidine *
    • Chloroform *
    • Benzidine *
    • Benzene *
    • Vinyl chloride *
    • Arsenic
    • Formaldehyde *


  • Mutagens are chemical and physical agents that induce mutations in DNA and in living cells. This affects the genetic system in such a way as to cause cancer or hereditary changes in chromosomes. Individuals exposed to chemicals with mutagenic properties may develop genetic damage to the extent that future offspring will be affected.
  • Known mutagens should not be used by students in our high school lab.
  • Examples of Mutagens:
    • Arsenic
    • Ethidium Bromide
    • Ionizing Radiation (gamma, x-rays)
    • Alkylating agents (e.g., dimethyl sulfate)


  • Teratogens are chemical and physical agents that interfere with normal embryonic development. Teratogens differ from mutagens in that there must be a developing fetus. Damage to the fetus (embryo) is most likely to occur early in pregnancy, during the first 8 - 10 weeks. Teratogens may produce congenital malformations or death of the fetus without inducing damage to the pregnant woman.
  • Known Teratogens should not be used by students in our high school lab.
  • Three identified Teratogens:
    • Dibromochloropropane
    • Lead
    • Ethylene oxide
  • Other materials associated with reproductive health disorders:
    • Antimony
    • Carbon disulfide
    • Polychlorinated biphenols (PCBs)
    • Nitrous oxide
    • Formaldehyde
    • Ethylene dibromide
Specific Hazard
Corrosive Materials:
  • Corrosive chemicals can burn, irritate, or destructively attack living tissue. When inhaled or ingested, lung and stomach tissue are affected.
  • Materials with corrosive properties can be either acidic (low pH) or basic (high pH).
    • Corrosive gases -- are readily absorbed into the body through skin contact and inhalation.
    • Corrosive liquids -- are frequently used in the laboratory and have a high potential to cause external injury to the body.
    • Corrosive solids -- cause delayed injury. Because corrosive solids dissolve rapidly in moisture on the skin and in the respiratory system, the effects of corrosive solids depend largely on the duration of contact.
  • Examples of commonly-used corrosives:
    • sulfuric acid
    • hydrochloric acid
    • nitric acid
    • ammonium hydroxide
    • sodium hydroxide


  • An oxidizing agent is a chemical used to provide oxygen for chemical reactions. Oxidizers spontaneously evolve oxygen at room or slightly elevated temperatures, and can explode violently when shocked or heated. Because they possess varying degrees of chemical instability, oxidizing agents are explosively unpredictable and, therefore, represent a particularly hazardous safety threat.
  • Examples of oxidizing agents:
    • peroxides
    • hyperperoxides
Explosive Materials:
  • Explosive materials are chemicals that cause a sudden, almost instantaneous release of large or small amounts of pressure, gas, and heat when subjected to sudden shock, pressure, or high temperature.
  • Examples of commonly-used explosive chemicals:
    • acetylene
    • hydrogen
    • nitrogen containing compounds
    • ammonia
    • halogens
    • perchlorates
  • Metals of group IA react with water to release hydrogen gas and heat which is an explosive combination.

ANSI and OSHA use the following signs related to safety:

Major safety hazard

A hazard to safety

Possible hazard

Safety information

    A few other signs related to safety:

        no food or drink
        eye protection required
        radioactive materials
        cancer hazard
        restricted area

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