High-hazard Group H occupancies are characterized by an unusually high degree of explosion, fire, or health hazard compared to typical commercial and industrial uses. There is one common feature about Group H occupancies—they are designated as Group H based on excessive quantities of hazardous materials within the facility/building. Where the quantities of hazardous material stored or used in a building exceed their Maximum Allowable Quantity (MAQ), a Group H classification is necessary. On the other hand, where such quantities are not exceeded, a Group H classification is not required.
Because of the technical nature of the operations and materials found in Group H occupancies, several specific terms are defined by the IBC in Chapter 2.
Group H-1 occupancies are those buildings containing high-explosion hazard materials. Materials that have the potential for detonation must be housed in buildings regulated in a very special manner, and designed and constructed unlike any other occupancies described in the code. Examples of detonable materials include explosives and Class 4 oxidizers.
Group H-2 generally includes those occupancies that contain materials with hazards of accelerated burning or moderate explosion potential, including materials with deflagration hazards. Common occupancies included in this category are those operations where flammable or combustible liquids are used, mixed, or dispensed. The potential for a hazardous incident is increased because of the materials’ exposure to the surrounding area. Occupancies containing COMBUSTIBLE DUST may also be considered Group H-2, as dust in suspension, or capable of being put into suspension, in the atmosphere are a deflagration hazard. In the determination of occupancy classification for a facility where COMBUSTIBLE DUST is anticipated, a technical report and opinion must be provided to the building official that provides all necessary information for a qualified decision as to the potential hazards due to the combustible dust.
Buildings containing materials that present high-fire or heat-release hazards are classified as Group H-3 occupancies. Where flammable or combustible liquids are present in such occupancies, they must be stored in normally closed containers or used in low-pressure systems. Because of the enclosed nature of these liquids, the hazard level is not nearly as severe as it is for Group H-2 occupancies. Other hazardous materials, such as organic peroxides and oxidizers, based on their hazard classification, may also be used or stored in Group H-3 occupancies.
Group H-4 occupancies are those containing health-hazard materials such as corrosives and toxics. Section 202 defines “Health hazards” as those “chemicals for which there is statistically significant evidence that acute or chronic health effects are capable of occurring in exposed persons.” Quite often, a material considered a health hazard also possesses the characteristics of a physical hazard. It is important that all hazards of materials be addressed.
Occupancies classified as Group H-5 are those uses containing semiconductor fabrication activities, including the ancillary research and development areas. The Group H-5 category was created in order to address the explosive and highly toxic materials used in semiconductor fabrication by providing specific requirements for the particular operations conducted, while at the same time providing a level that allows reasonable transaction of the fabrication process.
MAXIMUM ALLOWABLE QUANTITIES
Occupancy classifications of buildings containing hazardous materials are based on the maximum allowable quantities concept. Tables 307.1(1) and 307.1(2),
together with their appropriate footnotes, identify the maximum amounts of hazardous materials that may be stored or used in a control area before the area must be designated as a Group H occupancy. The maximum quantities of hazardous materials permitted in non–Group H occupancies vary for different states of materials (solid, liquid, or gas) and for different situations (storage or use). The allowable quantities are also varied based on protection that is provided, such as automatic sprinkler systems and storage cabinets.
CONTROL AREAS
Areas in a building that contain hazardous materials in amounts that do not exceed the maximum allowable quantities and that are properly separated from other areas
containing hazardous materials are called control areas. Any combination of hazardous materials, up to the maximum allowable quantities, is permitted in a control area. A control area may be an entire building or only a portion. It can be part of a story, an entire story, or even include multiple stories. A control area is classified, based on its use, as other than Group H, as its sole purpose is to avoid a Group H classification. The control-area method is based on the concept of fire-resistance-rated compartmentation. It regulates quantities of hazardous materials per compartment (control area) rather than per building. The limit for the entire building, using control areas, is then established by limiting the total number of control areas allowed per story and the quantities of hazardous materials in each control area.
The control-area concept was introduced to regulate buildings of different sizes consistently. It is based on the premise that the storage and use of limited quantities of hazardous materials (not exceeding MAXIMUM ALLOWABLE QUANTITIES) in areas that are separated from each other by FIRE-RESISTANCE-RATED SEPARATIONS do not substantially increase the risk to the occupants or change the character of the building to that of a hazardous occupancy, subject to a limitation on the number of control areas. Fire-resistive separations are relied on to minimize the risk of having multiple control areas involved simultaneously during an emergency. There is no special occupancy designation for a control area.