December 14, 2023
From the 2021 UPC Illustrated Training Manual, Chapter 12, FUEL GAS PIPING
1213.6 Purging Requirements. The purging of piping shall be in accordance with Section 1213.6.1 through Section 1213.6.3. [NFPA 54:8.3]
The purging requirements for purging indoors and outdoors provide increased safety procedures including gas detection, monitoring, and the location of discharge points. Purging requirements are specified depending upon the size of the piping system in terms of pipe diameter/length and operating pressure. The pipe diameter/length and pressure criteria are selected to distinguish between large commercial systems (industrial systems) and small commercial systems (including residential systems). Large systems have pipe volumes or potential for higher flow rates that require procedures to ensure that large volumes of fuel gases are not released indoors and that flammable mixtures do not occur within the piping itself. Installers of these complex systems deal with considerably more variables that may result in a higher potential for discharge of large gas volumes during purging operations. All large systems are required to be purged outdoors and the use of a combustible gas indicator is mandated. For smaller systems, the purging requirements allow five options that have been shown to be effective and are widely used. These include purging directly to the outdoors; purging through the appliance’s burner; purging through a standalone burner; purging to the indoors using a combustible gas detector; and purging in accordance with the written purging procedures of a gas supplier. The purging requirements recognize that the gas supplier has been successfully conducting purging operations with their trained personnel. Installers of smaller systems have familiarity with purging these systems and the potential for discharge of large gas volumes during purging operation is low.
1213.6.1 Piping Systems Required to be Purged Outdoors. The purging of piping systems shall be in accordance with Section 1213.6.1.1 through Section 1213.6.1.5 where the piping system meets either of the following:
(1) The design operating gas pressure is greater than 2 psig (14 kPa).
(2) The piping being purged contains one or more sections of pipe or tubing meeting the size and length criteria of Table 1213.6.1. [NFPA 54:8.3.1]
1213.6.1.1 Removal from Service. Where existing gas piping is opened, the section that is opened shall be isolated from the gas supply and the line pressure vented in accordance with Section 1213.6.1.4. Where gas piping meeting the criteria of Table 1213.6.1 is removed from service, the residual fuel gas in the piping shall be displaced with an inert gas. [NFPA 54:8.3.1.1]
1213.6.1.2 Removal of Piping. Where piping containing gas is to be removed, the line shall be first disconnected from sources of gas and then thoroughly purged with air, water, or inert gas before cutting, or welding is done.
Residual gas fumes remaining in the fuel gas piping system must be removed when any type of repair or replacement occurs that will include fire or sparks. Although this subsection permits the use of air for purging, an inert gas or water may provide an increase in safety for larger volume systems. Cutting is not limited to flame cutting because mechanical methods, such as cutting with a chop saw, can produce sparks that can ignite a gas-air mixture.
1213.6.1.3 Placing in Operation. Where gas piping containing air and meeting the criteria of Table 1213.6.1 is placed in operation, the air in the piping shall first be displaced with an inert gas. The inert gas shall then be displaced with fuel gas in accordance with Section 1213.6.1.4. [NFPA 54:8.3.1.2] 1213.6.1.4 Outdoor Discharge of Purged Gases. The open end of a piping system being pressure vented or purged shall discharge directly to an outdoor location. Purging operations shall comply with all of the following requirements:
(1) The point of discharge shall be controlled with a shutoff valve.
(2) The point of discharge shall be located at least10 feet (3048 mm) from sources of ignition, at least 10 feet (3048 mm) from building openings and at least 25 feet (7620 mm) from mechanical air intake openings.
(3) During discharge, the open point of discharge shall be continuously attended and monitored with a combustible gas indicator that complies with Section 1213.6.1.5.
(4) Purging operations introducing fuel gas shall be stopped when 90 percent fuel gas by volume is detected within the pipe.
(5) Persons not involved in the purging operations shall be evacuated from all areas within 10 feet (3048 mm) of the point of discharge. [NFPA 54:8.3.1.3]
1213.6.1.5 Combustible Gas Indicator. Combustible gas indicators shall be listed and calibrated in accordance with the manufacturer’s instructions. Combustible gas indicators shall numerically display a volume scale from 0 percent to 100 percent in 1 percent or smaller increments. [NFPA 54:8.3.1.4]
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Last modified: December 14, 2023