NFPA 13 Hazard classification.
Hazard classification hierarchy
The requirements contained in NFPA 13 are keyed to
the hazard classification. Section 2-1 in the 1999
edition of NFPA 13 indicates there are three basic
hazard classifications used in the design of sprinkler
systems. These three hazard classifications are as
follows:
• Light Hazard
• Ordinary Hazard
• Extra Hazard
This same section in NFPA 13 also indicates that
the ordinary hazard classification is divided into
two sub-classifications an ordinary group 1 hazard
and an ordinary group 2 hazard. Similarly, the extra
hazard classification is also divided into two sub-classifications
— an extra group1 hazard and an extra group
2 hazard.
The definitions of each of the hazard classifications
are also included in section 2-1 in NFPA13, which
defines hazard classification based upon a number
of occupancy characteristics.
These characteristics are as follows:
• The combustibility of contents.
• The quantity of combustibles.
• Rate of heat release.
• Storage height.
• Quantity of flammable and/or combustible
liquids.
NFPA 13 defines a light hazard occupancy
using the following description:
• Combustibility of the contents is low, and
• Quantity of the combustible is low, and
• Low rates of heat release.
The NFPA 13 definition an ordinary group
1 hazard is as follows:
• Combustibility of the contents is low, and
• Quantity of the combustibles is moderate,
and
• Moderate heat release rates, and
• Height of storage is 8 feet or less.
NFPA 13 defines an ordinary group 2 hazard
as follows:
• Combustibility of the contents is moderate
to high, and
• Quantity of the combustibles is moderate
to high, and
• Moderate to high rates of heat release, and
• Storage height is 12 feet or less.
The NFPA 13 definition of an extra group
1 hazard is as follows:
• Combustibility of the contents is very high,
and
• Quantity of the combustibles is very high,
and
• High rates of heat release, and
• Quantity of flammable and/or combustible
liquids small.
Finally, the NFPA 13 definition of an extra
group 2 hazard is as follows:
• Quantity of flammable or combustible liquids
is moderateto high, or
• Extensive shielding of the combustibles is
present.
Interpretation by example
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