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Calculating Standpipe Branch Lines

By Terin Hopkins posted Nov 29, 2021 11:30 AM

  

Standpipe Branch Lines

A standpipe branch line is simply a horizontal pipe connecting a standpipe to a single hose connection. Branch lines are typically added to meet travel distance requirements or where it is impracticable to install an additional vertical standpipe in a building. This pipe must be sized for the required flow and be at least 2 ½ inches in diameter. If the pipe extends more than 40 feet, measured along the pipe from the standpipe to the hose connection, a control valve must be provided. This control valve allows for isolation of the branch line for testing and maintenance without causing interruption to the rest of the system.

Calculating Flow Requirements

A single hose connection on a branch line is usually considered to be an extension of that standpipe without additional flow calculation requirements. In this configuration, the additional required flow is considered inconsequential. However, there is an exception to this rule, when multiple branch lines with single hose connections are installed on multiple floors from the same standpipe replicating an additional vertical standpipe. When a standpipe is replicated on floors using branch lines, they must be treated as if they are additional standpipes being supplied. This arrangement requires the branch lines to be considered an additional standpipe and increases the overall hydraulic system demand by 250 gpm.  

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An example is a building with two stairways with one standpipe in each stairway.  Both standpipes are equipped with branch lines to an additional hose connection on each floor to meet travel distance requirements. These branch lines and hose connections replicate additional standpipes without a vertical standpipe and would be considered as additional standpipes for the purpose of calculating the required flow.  This would require the two most remote hose connections on both standpipes to be calculated, and a system demand of 1,000 gpm when the building is protected throughout, in accordance with NFPA 13.  250 gpm from hose connections A, B, C and D is required.

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Horizontal Standpipe

If two or more hose connections are added to the branch line, it becomes a horizontal standpipe and must be calculated as an individual standpipe. This calculation is done at a higher 750 gpm demand to accommodate the tactical fire department hose line deployment from horizontal standpipes. The configuration is based on three hose lines being simultaneously deployed from a single standpipe level, unlike the strategies of vertical standpipes, where the use of two or more is commonly used allowing 500 gpm with the additional standpipe flow requirement of 250 gpm.  Horizontal standpipes are required to be a minimum of 4-inch pipe to meet the higher demand and must also have a control valve for isolation.

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This would require the three most remote hose connections on the horizontal standpipe to be calculated at 750 gpm, and an additional 250 gpm for each additional standpipe to a maximum of 1,000 gpm in a building protected throughout, in accordance with NFPA 13. Buildings not protected or designed to NFPA 13R require a maximum flow of 1,250 gpm.

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Mar 02, 2022 06:31 PM

Great explanation