Wisconsin Administrative Code › Department of Safety and Professional Services › SPS 301-399 - Safety, Buildings, and Environment › SPS 326-360 - General, Part II › Chapter SPS 340 - Gas systems › Subchapter IX - Liquefied Hydrogen Systems › Appendix - Appendix

Current through June 24, 2024
The material contained in this appendix is for
						clarification purposes only and is numbered to correspond to the number of the
						rule as the rule appears in the text of this chapter.
A-340.52 (1) (a) The process of purging gas piping of
						fuel gas or charging gas piping that is full of air with fuel gas must be
						performed in a manner that will minimize the potential for a flammable mixture
						to be developed within the piping. Also, a significant amount of flammable gas
						should not be released within a confined space. Natural gas and propane
						suppliers add a distinctive odor to their gas to aid in its detection. However,
						when a new system is brought into service and non-odorized gas is detected, the
						company supplying the gas should be informed of the situation to determine what
						action should be taken.
(b)
1. Section
						SPS 340.52(1) (b)
						1. describes the characteristics of gas
						piping systems that are required to be purged only to the outdoors. The
						criteria were selected to distinguish between piping systems located in
						industrial, large commercial, and large multifamily buildings from those
						located in light commercial and smaller residential buildings. The gas piping
						systems installed in industrial, large commercial, and large multifamily
						buildings are considered to be larger, more complex systems for the purposes of
						defining their purging requirements. Because of their larger pipe volumes or
						potential for higher flow rates, these systems 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.
						Specific occupancy categories such as industrial, manufacturing, commercial,
						and large multifamily were not included in the fuel gas code. Building codes
						define these occupancies for the purpose of construction and safety
						requirements. There is no general relation between the occupancy types, as
						defined by building codes, and the size of gas piping system to be installed in
						that occupancy. The gas piping size and operating pressure are based on the
						nature of the piping system and gas appliances to be installed and are not
						dependent upon a building's occupancy type or classification.
3. It is recommended that the oxygen levels in the piping
						be monitored during the purging process to determine when sufficient inert gas
						has been introduced. The manufacturer's instructions for monitoring instruments
						must be followed when performing purge operations.
5. Combustible gas indicators are available with
						different scales. For purging, it is necessary to use the percent gas in air
						scale and to follow the manufacturer's operating instructions. The percent LEL
						(lower explosive limit) scale should not be used as it is not relevant to
						purging.
(c)
1. The criteria were selected to describe typical gas
						piping systems located in light commercial and the smaller residential family
						buildings. Gas piping systems installed in these buildings are considered to be
						smaller and less complex systems for the purposes of defining their purging
						requirements. Installers have familiarity with purging these systems and the
						potential for discharge of large gas volumes during purging operations is low.
						Also see paragraph (b) 1. above.
2. Where small piping systems contain air and are purged
						to either the indoors or outdoors with fuel gas, a rapid and uninterrupted flow
						of fuel gas must be introduced into one end of the piping system and vented out
						of the other end so as to prevent the development of a combustible fuel and air
						mixture. Purging these systems can be done either using a source of ignition to
						ignite the fuel gas or by using a listed combustible gas indicator that can
						detect the presence of fuel gas.