High-hazard Group H occupancies are characterized by a greater degree of explosion, fire, or health hazard than typical commercial and industrial uses. There is one common feature of Group H occupancies: they are designated as Group H because they contain excessive quantities of hazardous materials. Where the quantities of hazardous material stored or used in a building exceed those set forth in Section 307 (High-Hazard Group H), a Group H classification is warranted. On the other hand, where such quantities are not exceeded, a Group H classification is not necessary.
Group H-1 occupancies are buildings that contain high-explosive hazard materials. Materials that have the potential to detonate 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 occupancies that contain materials with a high risk of accelerated burning or moderate explosion potential, including deflagration hazards. Common occupancies in this category include operations where flammable or combustible liquids are used, mixed, or dispensed. The potential for a hazardous incident is increased due to the materials’ exposure to the surrounding environment. Occupancies containing combustible dusts may also be considered as Group H-2, as dusts in suspension, or capable of being put into suspension, in the atmosphere are a deflagration hazard.
Group H-3 covers buildings containing materials that pose high fire or heat-release hazards. 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 in Group H-2 occupancies. Other hazardous materials, such as organic peroxides and oxidizers, may also be used or stored in Group H-3 occupancies, depending on their hazard classification.
Group H-4 occupancies contain health-hazard materials, such as corrosives and toxins. The code 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 poses a physical hazard. It is important that all hazards of materials be addressed.
Occupancies classified as Group H-5 are those uses that contain semiconductor fabrication activities, including 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.
Source: IBC 2021