Occupancy, Building Codes and Fire Ratings

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Building codes

Building codes define the allowable size of a building, both in area and in height. Based on the construction type and the occupancy use group. A building structure constructed of combustible materials would be limited in both size and height, more than a building with non-combustible materials (skyscraper).  It is also safer to fight fires in such buildings.  The two main building codes which dictate this are the IBC (international building code) and the NFPA (National Fire Protection Association’s codes NFPA 5000 Building Construction and Safety Code and NFPA 101 Life Safety Code ).

Building codes define requirements for fire ratings, fire protection, egress, and accessibility.  This affects construction materials and methods, whether or not a building will be sprinklered, or involve any other special fire suppression systems.

type-of-construction-and-allowable-building-area-and-height

Occupancy-and-Building-Code-IBC-table-1004.1-hi-res

Use and Occupancy

The intended use or “occupancy” of a building provides the first major design consideration.  Each occupancy relates to a specific type of concern such as the potential for panic in facilities, or young persons in need of adult guidance (such as a daycare).  The IBC has 10 major types of occupancy, you can see here to the right.

Group A–Assembly: in facilities where more than 50 people gather for a common purpose, where there is a danger of panic, requires that the doors swing out in the direction of egress.

Group B–Business: Professional and service facilities as well as drinking and dining facilities for less than 50 people.

Group E– Educational: Where six or more children that require adult supervision during an emergency.  Education Facilities through 12th grade are anticipated to have trained faculty and staff who know through fire drills and proper procedures to ensure life safety for all school occupants.

Group F–Factory: Factories with moderate and low hazard materials and standard industrial use—this shares many Group B requirements.

Group H — Hazardous: Facilities  that involve the manufacturing, processing, generation, or storage of materials that constitute a physical or health hazard such as explosive, combustible, corrosive, or toxic materials that have special limitations and restrictions.

Group I — Institutional: These are facilities that house people day and night who are supervised 24hrs a day, either due to medical problems or due to incarceration for the public welfare such as hospitals, nursing homes, nurseries, sanitariums, jails, prisons and reform schools.

Group M — Mercantile: Facilities for display and sale of merchandise presently share the same requirements as Group B–Business.

Group R — Residential:  These are facilities used for sleeping other than institutional facilities including temporary  hotels (R-1) and permanent facilities such as apartments and dormitories (R-2)  and also one and two family dwelling units (R-3).

Example: Occupant load is dependent on number of square feet and occupancy type.  So for a business occupancy with 3,000 s.f. at 100 s.f. per occupant would equal 30 occupants.

Type of Construction

There are two types of construction: combustible and non-combustible.  Each will have a different fire ratings depending on methods and materials used ( example: 4,3,2,or 1 hour fire rating).

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Type I and II are considered non-combustible. Requiring structural components to be made of steel, concrete, masonry, but not wood. This type of construction might not have fire ratings, depending on occupant use.

Type III, Type IV, and Type V construction is combustible.  Combustible structural materials give less time for firemen; depending on how long the structural components can be expected to continue to support their loads without collapse after a fire starts.

 

Fire-Rated Construction

Non-combustible buildings are often allowed unlimited height and area because the fire personnel can fight the fire from inside the building without danger of collapse.  A non-rated building could collapse in less than one hour after the fire began; this is essential that the building have access to a “public way” so the firemen can fight the fire from the exterior of the building.  Some of the safest occupancies (Group B–Business) are limited to five stories for one-hour fire-rated and non-fire rated construction; another floor (6 stories) can be added if an approved automatic sprinkler system is provided.

Typical 1 Hour Fire-Rated Wall

TYPICAL 1 HOUR FIRE RATED WALL

Typical 2 Hour Fire-Rated Wall

TYPICAL 2 HOUR FIRE-RATED WALL NON-COMBUSTIBLE

[source: GA 600 Fire Resistant Design Manual]

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