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What are the NFPA Ratings?

The NFPA system was developed for short-term, often acute exposure to chemicals under conditions of fires or spills. The ratings are intended to provide fire-fighting and evacuation information.

Note also that the NFPA system for ratings for hazardous chemicals was updated in August, 1996. The category "Reactivity" was replaced with "Instability". Consult NFPA 704, 1996 for more detailed information on the why this update was made. You can purchase this guide by calling 800 344-3555.

The NFPA ratings criteria can be summarized as follows:

Health

Materials that, under emergency conditions, can be lethal. The following criteria shall be considered when rating materials:

  • Gases whose LC for acute inhalation toxicity is less than or equal to 1000 parts per million (ppm);
  • Any liquid whose saturated vapor concentration at 68 degrees F (20 degrees C) is equal to or greater than ten times its LC for acute inhalation toxicity, if its LC is less than or equal to 1000 parts per million (ppm);
  • Dusts and mists whose LC for acute inhalation toxicity is less than or equal to 0.5 milligrams per liter (mg/L);
  • Materials LD for acute dermal toxicity is less than or equal to 40 milligrams per kilogram (mg/kg);
  • Materials whose LD for acute oral toxicity is less than or equal to 5 milligrams per kilogram (mg/kg).

Materials that, under emergency conditions, can cause serious or permanent injury. The following criteria shall be considered when rating materials:

  • Gases whose LC for acute inhalation toxicity is greater than 1000 parts per million (ppm), but less than or equal to 3000 parts per million (ppm);
  • Any liquid whose saturated vapor concentration at 68 degrees F (20 degrees C) is equal to or greater than its LC for acute inhalation toxicity, if its LC is less than or equal to 3000 parts per million (ppm) and that does not meet the criteria for degree of hazard 4;
  • Dust and mist whose LC for acute inhalation toxicity is greater than 0.5 milligrams per liter (mg/L), but less than or equal to 2 milligrams per liter (mg/L);
  • Materials whose LD for acute dermal toxicity is greater than 40 milligrams per kilogram (mg/kg), but less than or equal to 200 milligrams per kilogram (mg/kg);
  • Materials that are corrosive to the respiratory tract;
  • Materials that are corrosive to the eye or cause irreversible corneal opacity;
  • Materials that are severely irritating and/or corrosive to skin;
  • Materials whose LD for acute oral toxicity is greater than 5 milligrams per kilogram (mg/kg), but less than or equal to 50 milligrams per kilogram (mg/kg).

Materials that, under emergency conditions, can cause temporary incapacitation or residual injury. The following criteria shall be considered when rating materials:

  • Gases whose LC for acute inhalation toxicity is greater than 3000 parts per million (ppm), but less than or equal to 5000 parts per million (ppm);
  • Any liquid whose saturated vapor concentration at 68 degrees F (20 degrees C) is equal to or greater than one-fifth (1/5) its LC for acute inhalation toxicity, if its LC is less than or equal to 5000 parts per million (ppm) and that does not meet the criteria for either degree of hazard 3 or degree of hazard 4;
  • Dust and mists whose LC for acute inhalation toxicity is greater than 2 milligrams per liter (mg/L), but less than or equal to 10 milligrams per liter (mg/L);
  • Materials whose LD for acute dermal toxicity is greater than 200 milligrams per kilogram (mg/kg), but less than or equal to 1000 milligrams per kilogram (mg/kg);
  • Materials that are respiratory irritants;
  • Materials that cause irritating but reversible injury to the eyes;
  • Materials that are primary skin irritants or sensitizers;
  • Materials whose LD for acute oral toxicity is greater than 50 milligrams per kilogram, but less than or equal to 500 milligrams per kilogram (mg/kg).
   Materials that, under emergency conditions, can cause significant irritation. The following criteria shall be considered when rating materials:
  • Gases and vapors whose LC for acute inhalation toxicity is greater than 5000 parts per million (ppm), but less than or equal to 10,000 parts per million (ppm);
  • Dust and mists whose LC for acute inhalation toxicity is greater than 10 milligrams per liter (mg/L), but less than or equal to 200 milligrams per kilogram (mg/kg);
  • Materials whose LD or acute dermal toxicity is greater than 1000 milligrams per kilogram (mg/kg), but less than or equal to 2000 milligrams per kilogram (mg/kg);
  • Materials that are slightly irritating to the respiratory tract, eyes and skin;
  • Materials whose LD for acute oral toxicity is greater than 500 milligrams per kilogram (mg/kg), but less than or equal to 500 milligrams per kilogram (mg/kg), but less than or equal to 2000 milligrams per kilogram (mg/kg).
   Materials that, under emergency conditions would offer no      hazard beyond that of ordinary combustible materials. The   following criteria shall be considered when rating materials:
  • Gases and vapors whose LC for acute inhalation toxicity is greater than 10,000 parts per million (ppm);
  • usts and mists whose LC for acute inhalation toxicity is greater than 200 milligrams per liter (mg/L);
  • Materials whose LD for acute dermal toxicity is greater than 2000 milligrams per kilogram (mg/kg);
  • Materials whose LD for acute oral toxicity is greater than 2000 milligrams per kilogram (mg/kg);
  • Essentially nonirritating to the respiratory tract, eyes and skin.

Flammability

   Materials that will rapidly or completely vaporize at atmospheric pressure and normal ambient temperature or that are readily dispersed in air, and which will burn readily. This includes:
  • Flammable gases;
  • Flammable cryogenic materials;
  • Any liquid or gaseous material that is liquid while under pressure and has a flash point below 73 degrees F (22.8 degrees C) and a boiling point below 100 degrees F (37.8 degrees C) (i.e., Class 1A liquids);
  • Materials that ignite spontaneously when exposed to air;
  • Liquids and solids that can be ignited under almost all ambient temperature conditions.
   Materials in this degree produce hazardous atmospheres with air under almost all ambient temperatures or, though unaffected by ambient temperatures, are readily ignited under almost all conditions. This includes:
  • Liquids having a flash point below 73 degrees F (22.8 degrees C) and having a boiling point at or above 100 degrees F (37.8 degrees C) and those liquids having a flash point at or above 73 degrees F (22.8 degrees C) and below 100 degrees F (37.8 degrees C) (i.e., Class 1B and Class 1C liquids);
  • Materials that on account of their physical form or environmental conditions can form explosive mixtures with air and that are readily dispersed in air;
  • Materials that burn with extreme rapidity, usually by reason of self-contained oxygen (e.g., dry nitrocellulose and many organic peroxides).
   Materials that must be moderately heated or exposed to relatively high ambient temperatures before ignition can occur. Materials in this degree would not under normal conditions form hazardous atmospheres with air, but under high ambient temperatures or under moderate heating might release vapor in sufficient quantities to produce hazardous atmospheres with air. This includes:
  • Liquids having a flash point at or above 100 degrees F (37.8 degrees C) and below 200 degrees F (93.4 degrees C) (i.e., class II and Class IIIA liquids);
  • Solid materials in the form of coarse dusts that burn rapidly but that generally do not form explosive atmospheres with air;
  • Solid materials in a fibrous or shredded form that burn rapidly and create flash fire hazards, such as cotton, sisal, and hemp;
  • Solids and semisolids that readily give off flammable vapors.
   Materials that must be preheated before ignition can occur. Materials in this degree require considerable preheating, under all ambient temperature conditions, before ignition and combustion can occur. This includes:
  • Materials that will burn in air when exposed to a temperature of 1500 degrees F (815.5 degrees C) for a period of 5 min. or less;
  • Liquids, solids, and semisolids having a flash point at or above 200 degrees F (93.4 degrees C) (i.e., Class IIIB liquids);
  • Liquids with a flash point greater than 95 degrees F (35 degrees C) that do not sustain combustion when tested using the Method of Testing for Sustained Combustibility, per 49 CFR Part 173 Appendix H, or the UN Recommendations on the Transport of Dangerous Goods, 8th Revised Edition;
  • Liquids with a flash point greater than 95 degrees F (35 degrees C) in a water-miscible solution or dispersion with a water noncombustible liquid/solid content of more than 85 percent by weight;
  • Liquids that have no fire point when tested by ASTM D 92, Standard Test Method for Flash Point and Fire Point by Cleveland Open Cup, up to the boiling point of the liquid or up to a temperature at which the sample being tested shows an obvious physical change;
  • Most ordinary combustible materials.
   Materials that will not burn. This includes any material that will not burn in air when exposed to a temperature of 1500 degrees F (815.5 degrees C) for a period of 5 min.

Reactivity/Instability

   Materials that in themselves are readily capable of detonation or explosive decomposition or explosive reaction at normal temperatures and pressures. This includes materials that are sensitive to localized thermal or mechanical shock at normal temperatures and pressures. This includes:
  • Materials that have an instantaneous power density (product of heat or reaction and reaction rate) at 482 degrees F (250 degrees C) of 1000 W/mL or greater.
   Materials that in themselves are capable of detonation or explosive decomposition or explosive reaction, but that require a strong initiating source or that must be heated under confinement before initiation. This includes:
  • Materials that have an instantaneous power density (product of heat of reaction and reaction rate) at 482 degrees F (250 degrees C) at or above 100 W/mL and below 1000 W/mL;
  • Materials that are sensitive to thermal or mechanical shock at elevated temperatures and pressures;
  • Materials that react explosively with water without requiring heat or confinement.
   Materials that readily undergo violent chemical change at elevated temperatures and pressures. This includes:
  • Materials that have an instantaneous power density (product of heat of reaction and reaction rate) at 482 degrees F (250 degrees C) at or above 10W/mL and below 100 W/mL;
  • Materials that react violently with water or form potentially explosive mixtures with water.
   Materials that in themselves are normally stable, but that can become unstable at elevated temperatures and pressure. This includes:
  • Materials that have an instantaneous power density (product of heat of reaction and reaction rate) at 482 degrees F (250 degrees C) at or above 0.01 W/mL and below 10W/mL;
  • Materials that react vigorously with water, but not violently;
  • Materials that change or decompose on exposure to air, light, or moisture.
NFPAbul0r.gif (364 bytes)   Materials that in themselves are normally stable, even under fire conditions. This includes:
  • Materials that have an instantaneous power density (product of heat of reaction and reaction rate) at 482 degrees F (250 degrees C) below 0.01 W/mL;
  • Materials that do not react with water;
  • Materials that do not exhibit an exotherm at temperatures less than or equal to 932 degrees F (500 degrees C) when tested by differential scanning calorimetry.

Special Hazard

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(No Special Hazard
)

ACID.gif (498 bytes)        
(Acid *)

ALK.gif (435 bytes)        
(Alkali *)

COR.gif (481 bytes)        
(Corrosive *)

OX.gif (541 bytes)        
(Oxidizer)

NoWatOx.gif (1325 bytes)           
(Oxidizer and Use No Water)

Radioact.gif (608 bytes)        
(Radioactive *)

NoWater.gif (529 bytes)        
(Use No Water)


* Not referenced in NFPA 704

NFPA Rating Guide

Rating Number Health Hazard Flammability Hazard Instability Hazard Rating Symbol Special Hazard
4 Can be lethal Will vaporize and readily burn at normal temperatures May explode at normal temperature and pressures Alkaline Alkaline
3 Can cause serious or permanent injury Can be ignited under almost all ambient temperatures May explode at high temperature or shock Acidic Acidic
2 Can cause temporary incapacitation or residual injury Must be heated or high ambient temperature to burn Violent chemical change at high temperatures or pressures Corrosive Corrosive
1 Can cause significant irritation Must be preheated before ignition can occur Normally stable. High temperatures make unstable Radioactive Radioactive
0 No Hazard Will not burn Stable Reacts to Water Reacts violently or explosively with water

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