Wis. Admin. Code Department of Safety and Professional Services, SPS 301-399, SPS 326-360, ch. SPS 340, subch. IX, Appendix
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.
Wis. Admin. Code Department of Safety and Professional Services, SPS 301-399, SPS 326-360, ch. SPS 340, subch. IX, Appendix