NFPA 704 special hazard quadrant

The bottom quadrant carrying a letter code.

Also known as: White quadrant fire diamond, Letter code quadrant

Engineering & technicalSafety & hazardStandard profile

Meanings

The bottom quadrant of the NFPA diamond, carrying a letter code for a specific hazard rather than a rating.

Officially standardisedVerified fact
Carries a letter code for a specific hazard on the NFPA diamond, such as reaction with water or the presence of an oxidiser.
Contexts: Public information
Officially standardisedVerified fact
Is the only quadrant that names a hazard rather than grading one, so it breaks the diamond's own pattern and does so deliberately.
Contexts: Public information

The lower of four small diamonds, left pale and carrying a letter or a struck-through symbol rather than a digit.

IdentityHigh confidence: High confidence because the identity is defined by a current official standard, but only a single source has been found so far.
Historical originLow confidence: Low confidence because the historical origin is documented in encyclopedic references, but only a single source has been found so far, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is defined by a current official standard, but only a single source has been found so far.
Visual matchModerate confidence: Moderate confidence because the visual match is documented in encyclopedic references, but only a single source has been found so far.

NFPA 704, Standard System for the Identification of the Hazards of Materials
National Fire Protection Association · retrieved 2026-08-25
The standard defining the four-quadrant hazard diamond used on fixed installations in the United States. Cited for what each quadrant and rating means. Records are descriptive; they are not emergency response guidance and no record should be used to assess a hazard.

Last reviewed 2026-08-25

Meanings

The bottom quadrant of the NFPA diamond, carrying a letter code for a specific hazard rather than a rating.

Officially standardisedVerified fact

Carries a letter code for a specific hazard on the NFPA diamond, such as reaction with water or the presence of an oxidiser.

Officially standardisedVerified fact

Is the only quadrant that names a hazard rather than grading one, so it breaks the diamond's own pattern and does so deliberately.

Confidence

IdentityHigh confidence: High confidence because the identity is defined by a current official standard, but only a single source has been found so far.
Historical originLow confidence: Low confidence because the historical origin is documented in encyclopedic references, but only a single source has been found so far, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is defined by a current official standard, but only a single source has been found so far.
Visual matchModerate confidence: Moderate confidence because the visual match is documented in encyclopedic references, but only a single source has been found so far.

Sources

NFPA 704, Standard System for the Identification of the Hazards of Materials
National Fire Protection Association · retrieved 2026-08-25
The standard defining the four-quadrant hazard diamond used on fixed installations in the United States. Cited for what each quadrant and rating means. Records are descriptive; they are not emergency response guidance and no record should be used to assess a hazard.

Last reviewed 2026-08-25