Hazard Class Definition of Fire Sprinkler Systems in Chicago

Michael Tobias
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    The threat of a fire breaking out at any time due to the slightest error is real, given the reliance on gas and electrically powered appliances. Fire sprinkler systems are used as part of active fire protection strategy of a building or facility to detect a fire and extinguish it before any damage is caused. As an active form of fire protection they form part of any Life Safety Evaluations prepared for a building or facility by a professional employed to conduct such an inspection. In Chicago, these systems are designed, according to their hazard classification, to meet required national, state and local fire protection code.

    Here we describe the regulatory backdrop of hazard class definition of fire sprinkler systems in the Chicago, define the hazard classes available there and a key challenge to this classification.

    Regulatory Backdrop to Hazard Class Definition of Fire Sprinkler Systems in Chicago

    In the US, sprinkler systems are designed to meet regulatory requirements of the National Fire Protection Association (NFPA) code, of which hazard class designation for sprinkler systems forms a part in Chapter 13. In Chicago, this is defined in the Municipal Code of Chicago Title 15 / Chapter 15-16. The subject is covered in more detail here for guidance purposes. Note recourse should be made to the current editions on the codes prior to design, specification and installation of a fire sprinkler system.

    Defining a sprinkler system hazard class in Chicago

    In Chicago the definition of a fire sprinkler system’s hazard class determines the characteristics of its installation (in regards of specification of water supply, fire pump quantity, sprinkler number and so on). Light hazard and Extra Hazard classes depend on defined occupancy use. Each hazard classification type influences sprinkler design.

    The hazard class to which the sprinkler system is to be designed, should be determined before starting sprinkler system design and installation work.

    Buildings can contain one or more of the following hazard classes relating to NFPA and Municipal Code of Chicago.

    Light Hazard class

    In Chicago, the light hazard class relates to non-industrial buildings with low fire load, be they any of the following designated occupancy classes:

    (A-2) Multiple Dwellings, (B) Institutional, (C) Assembly or (E) Business. 

    Sprinkler systems for this class are designed in accordance with NFPA light hazard classification where:

    • Quantity of combustibles is low and/or
    • Combustibility of contents is low and
    • Low rates of heat release expected.

    Areas of such occupancies used for storage, garage, building maintenance or shop purposes shall be sprinkled in accordance with the provisions of the Municipal Code of Chicago for industrial occupancies. In buildings of mixed occupancy the provision for light hazard sprinkler systems shall apply only to those portions of the building occupied by the above occupancies.

    Ordinary Hazard class

    The ordinary hazard class relates to trading and industrial buildings with medium fire loads. Sprinkler systems for this class are designed in accordance with NFPA ordinary hazard classification.

    Group 1:

    • Quantity of combustibles is moderate
    • Combustibility of contents is low
    • Storage heights are 8 feet or under
    • Moderate rates of heat release expected.

    Group 2:

    • Quantity of combustibles is moderate to high
    • Combustibility of contents is moderate to high
    • Storage heights are 12 ft or under
    • Moderate to high rates of heat release expected.

    Extra Hazard Classes

    High hazard classification involves areas with a higher concentration of flammable materials, typically storage facilities where racking is used and chemical processes. These are high-risk areas that need more water to distinguish fire.

    Sprinkler systems for these classes are designed in accordance with NFPA high hazard classification in two categories:

    Group 1:

    • Combustibility of the contents is very high
    • Quantity of the combustibles is very high
    • High rates of heat release, and
    • Quantity of flammable and/or combustible liquids small.

    Group 2:

    • Quantity of flammable or combustible liquids is moderate to high
    • Extensive shielding of the combustibles is present.

    According to the Municipal Code of Chicago, the following classes of occupancy when provided with sprinkler systems shall have such sprinkler systems designed in accordance with extra hazard and extra density classifications of this code.

    • Industrial units (G-2): Paper processing * Plastics processing * Plywood / particle board manufacturing * Rubber reclaiming / milling * Tire manufacturing * Upholstering with plastic foam
    • Storage units (H-2): Aircraft hangars * Alcoholic beverages containing over 20% alcohol * Baled rags * Flammable liquids * Furniture storage warehouse * Freight warehouse * Paper / paper products warehouse * Rubber tire storage
    • Hazardous use units: Occupancies primarily involved in processing mixing, storing, dispensing volatile flammable liquids * Pyroxylin plastic manufacturing / processing * Cotton picking / opening operations

    Challenges of hazard classification

    Classification is not without its challenges, particularly where classification of storage facilities is concerned. Correct classifying stored goods is a vital step in code-compliant sprinkler system design for storage facilities.

    According to the NFPA a commodity is the “combination of products, packaging material, and container.” Thus, not simply the item being stored but also its packaging, containers and pallets. Misunderstanding of this can lead to mis-classification and sprinkler systems that are under-designed.

    As they change, fire properties of commodities may evolve too. Commodities that were classified a certain way previously may not be classified the same way today, and fire protection design, including sprinkler system design, may have to change in response. It’s therefore important to reassess the fire risk of them when this happens and anticipate any implications of such changes for storage facilities and that the Engineer of Record understands what the source of information is for any given storage project and that it is up to date.

    Taking these issues into consideration will help sprinkler system designers determine the appropriate commodity classification, a crucial step towards effective sprinkler performance, reduced risk, and reduced economic or at worst fatal human loss.

    End Note

    From this information surrounding hazard class definition of fire sprinkler systems in Chicago, it is apparent that classification is complex and not without challenges. Sprinkler systems can also form part of life safety evaluations, where recourse to a professional architect or engineer may be required. Engineers with experience of sprinkler engineering are well suited to provide this service.

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