The Harris County Fire Flow Calculator

 

 

Providing Harris County with Water Storage for Fire Protection

Harris County requires permits and plan submittals for new fire alarm and fire sprinkler systems to include providing the required water supply, the fire flow, for the building.

 

FIRE-FLOW: The flow rate of a water supply, measured at 20 pounds per square inch (psi) (138 kPa) residual pressure, that is available for fire fighting.

 

FIRE-FLOW CALCULATION AREA: The floor area, in square feet (m2) used to determine the required fire flow.

 

Link to Harris County Fire Flow worksheet:

The Harris County Fire Flow worksheet is based off of the National Fire Academy (NFA) method of calculating fire flow.

 

Needed fire flow = [(length x width) ÷ 3] x percent of involvement

 

Example: For a 30′ x 50′ building that’s 25 percent involved, the flow would be 30 x 50 = 1,500 square feet, divided by 3 = 500 x 0.25 = 125 GPM.

Houston Fire Code as Relevant to Fire Flow

 

507.1 Required water supply. An approved water supply capable of supplying the required fire flow for fire protection shall be provided to premises upon which facilities, buildings or portions of buildings are hereafter constructed or moved into or within the jurisdiction.

 

508.1 Required water supply. An approved water supply capable of supplying the required fire flow for fire protection shall be provided to premises upon which facilities, buildings or portions of buildings are hereafter constructed or moved into or within the jurisdiction. A water supply as otherwise required by this section will not be required if the responsible emergency services district or fire department provides a letter stating they can provide sufficient fire flow for the specific project.

 

2808.18 Fire protection response plan: • Local fire department is a participant in the plan • Local fire department has a copy of the fire prevention response plan 32 • Employees are trained and can perform their role in an emergency • Heavy equipment with trained operators to separate and work piles is on site or immediately available • Adequate water supply: fixed hydrants, portable tanks, ponds, other sources • Adequate pressure and flow rate at all locations on site (minimum of 250 GPM at 60 PSI)

Link to the City of Houston Fire Code: Link

One fire sprinkler can use on average eight gallons-per-minute (GPM). Most home fire sprinkler systems accommodate two simultaneous flowing sprinklers, with a minimum need of 16 GPM to supply them with water. The size of a house, local building requirements and the water source may require more sprinklers or be required at a higher pump rate. One or two sprinklers must flow for a minimum of 7-10 minutes, which can be provided by a well tank or a rainwater tank when sprinklers are not supplied by a water distribution system. Fire sprinkler systems that aren’t supplied enough by a utility water source, need an on hand water supply of at least 15% of the total required fire flow (but exact percentage is based on local authority requirements).

Additional water storage ensures that your property has water on hand for emergencies, typically with its own pump system that won’t go down in case of electricity failure. This becomes even more important, if not required, based on how rural the property location is.

 

Rural water distribution systems that are found to be inadequate to supply 16 GPM for fire sprinklers, would probably fall short of the minimum code-required plumbing demand, and it would surely fall far short of the 1,000+ GPM needed from fire hydrants to support a fire department extinguishing a fire in a home without a sprinkler system.

In order to figure out the exact fire flow requirements, refer to the local Fire and Building Codes, as well as refer to the local pre-inspection requirements. If fire flow must be measured in regards to the local Fire Code, the ICC International Code Council provides a chart to show fire flow requirements based on the of building construction and square footage. The ICC Construction Types that determine the fire flow, are listed in the drop-down below. The calculation uses the ICC minimum required fire-flow and flow duration for buildings.

TYPE I-A–Fire Resistive Non-combustible (Commonly found in high-rise buildings and Group I occupancies).

    • 3 Hr. Exterior Walls*
    • 3 Hr. Structural Frame
    • 2 Hr. Floor/Ceiling Assembly
    • 1 ½ Hr. Roof Protection

 

TYPE I-B–Fire Resistive Non-Combustible (Commonly found in mid-rise office & Group R buildings).

  • 2 Hr. Exterior Walls*
  • 2 Hr. Structural Frame
  • 2 Hr. Ceiling/Floor Separation
  • 1 Hr. Ceiling/Roof Assembly

 

TYPE II-A–Protected Non-Combustible (Commonly found in newer school buildings).

  • 1 Hr. Exterior Walls
  • 1 Hr. Structural Frame
  • 1 Hr. Floor/Ceiling/Roof Protection

 


 

TYPE II-B–Unprotected Non-Combustible (the Most common type of non-combustible construction used in
commercial buildings).

  • Building constructed of non-combustible materials but these materials have no fire resistance.

 

TYPE III-A–Protected Combustible (Also known as “ordinary” construction with brick or block walls and a
wooden roof or floor assembly which is 1-hour fire protected).

  • 2 Hr. Exterior Walls*
  • 1 Hr. Structural Frame
  • 1 Hr. Floor/Ceiling/Roof Protection

 

TYPE III-B–Unprotected Combustible (Also known as “ordinary” construction; has brick or block walls with a
wooden roof or floor assembly which is not protected against fire. These buildings are frequently found in
“warehouse” districts in older cities.)

  • 2 Hr. Exterior Walls*
  • No fire resistance for structural frame, floors, ceilings, or roofs.

 


 

TYPE IV–Heavy Timber (also known as “mill” construction; to qualify all wooden members must have a
minimum nominal dimension of 8 inches.)

  • 2 Hr. Exterior Walls*
  • 1 Hr. Structural Frame or Heavy Timber
  • Heavy Timber Floor/Ceiling/Roof Assemblies

 

TYPE V-A–Protected Wood Frame (Commonly used in the construction of newer apartment buildings; there is
no exposed wood visible.)

  • 1 Hr. Exterior Walls
  • 1 Hr. Structural Frame
  • 1 Hr. Floor/Ceiling/Roof

 

TYPE V-B–Unprotected Wood Frame (Examples of Type V-N construction are single-family homes and
garages. They often have exposed wood so there is no fire resistance.)

The following calculation uses the ICC Fire Flow based on the above construction types of square footage of the building. The chart below reflects the calculation as well.

We provide water storage for fire protection, with a full line of NFPA approved firefighting adapter and nozzle options. Get your best price on water storage with Pioneer Water Tanks America localized dealer and installation network.

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