When designing fire sprinkler systems, one of the most critical steps is determining the correct hazard classification for a building or area. This classification directly influences the required sprinkler system density, type, and spacing, ensuring the system is tailored to the fire risk present. Both the 2018 International Fire Code (IFC) and NFPA 13 provide guidance on how to classify occupancies and commodities, which is essential for code compliance and effective fire protection.
What Are Hazard Classifications?
Hazard classifications are categories that describe the relative fire risk of a building’s use or the materials stored within it. The most common classifications for non-storage occupancies are:
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Light Hazard
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Ordinary Hazard Group 1 (OH1)
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Ordinary Hazard Group 2 (OH2)
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Extra Hazard Group 1 (EH1)
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Extra Hazard Group 2 (EH2)
While “OH3” is not a standard NFPA 13 designation, the term is sometimes used informally to refer to higher-risk ordinary hazard occupancies or as a misnomer for extra hazard groups.
How Do IFC 2018 and NFPA 13 Define Hazard Classifications?
NFPA 13 is the primary standard for the installation of sprinkler systems and provides detailed definitions and examples for each hazard classification. The 2018 IFC references NFPA 13 for sprinkler system design and hazard classification.
According to NFPA 13:
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Ordinary Hazard Group 1 (OH1) includes occupancies with moderate fire loads and low combustibility, such as bakeries, laundries, and mechanical rooms.
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Ordinary Hazard Group 2 (OH2) covers occupancies with higher fire loads or combustibility, such as parking garages, machine shops, and mercantile spaces.
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Extra Hazard Groups are for occupancies with high fire loads or processes, such as manufacturing involving flammable liquids or plastics.
NFPA 13 provides annex lists of typical occupancies for each group. For example, “Ordinary hazard (Group 1) occupancies include uses and conditions similar to bakeries, beverage manufacturing, electric fire pump rooms, and mechanical rooms. Ordinary hazard (Group 2) occupancies include agricultural facilities, automobile parking garages, chemical plants, and machine shops” (13-2025).
The IFC 2018 defers to NFPA 13 for these definitions and requires that the hazard classification be determined as part of the sprinkler system design process.
Why Is Hazard Classification So Important?
The hazard classification determines:
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Sprinkler Density: The amount of water (in gallons per minute per square foot) that must be delivered over a specified area.
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Sprinkler Type: The kind of sprinkler head (standard spray, quick response, etc.) suitable for the hazard.
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Sprinkler Spacing: The maximum allowable distance between sprinklers, which varies based on hazard level and ceiling height.
For example, “the classification is considered in many states to be the most important aspect of fire protection system design, and an obligation of the responsible design professional. One reason many states require involvement of a responsible design professional is to ensure that the site-specific attributes of the project are recognized and properly addressed, which cannot be accomplished in a generic manner” (CAS-15107-M3D9J9: Occupancy Question).
How Are Classifications Determined?
Classification is based on:
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Combustibility of contents
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Quantity and arrangement of combustibles
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Expected heat release rate in a fire
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Building use and processes
NFPA 13 provides guidance and examples, but the final determination is the responsibility of the design professional, who must consider the specific characteristics of each space. For example, “all areas of a school (or other occupancy types) are not automatically assigned the same hazard classification as the main occupancy type and further investigation of the combustibility, quantities, and heat release rates of the contents in each area would need to be investigated” (EOD HB 2004-2022).
Impact on Sprinkler System Design
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OH1: Requires a minimum density of 0.15 gpm/ft² over the most hydraulically remote 1,500 ft².
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OH2: Requires a minimum density of 0.20 gpm/ft² over 1,500 ft².
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EH1/EH2: Require even higher densities and may have additional requirements for sprinkler types and spacing.
Sprinkler spacing and allowable obstructions also become more restrictive as the hazard classification increases.
Conclusion
Correctly classifying the hazard is essential for designing a compliant and effective fire sprinkler system. Both the 2018 IFC and NFPA 13 emphasize the importance of a thorough, site-specific evaluation by a qualified design professional. The hazard classification will dictate the system’s density, type, and spacing—ensuring that the fire protection matches the risk.
