Article 51 – Semiconductor Fabrication Facilities 5101.10.4 Continuous gas-detection systems 5101.10.4.1 General. A continuous gas-detection system shall be provided for HPM gases when the physiological warning properties of the gas are at a higher level than the accepted permissible exposure limit (PEL) for the gas and for flammable gases in accordance with Section 5101.10.4. 5101.10.4.2 Where required 5101.10.4.2.1 Fabrication areas. A continuous gas-detection system shall be provided for fabrication areas at locations in the fabrication area where gas is used or stored. 5101.10.4.2.2 HPM rooms. A continuous gas-detection system shall be provided in HPM rooms when gas is used in the room. 5101.10.4.2.3 Gas cabinets, exhausted enclosures and gas rooms. A continuous gas- detection system shall be provided in gas cabinets, exhausted enclosures and gas rooms. 5101.10.4.2.4 Corridors. When gases are transported in piping placed within the space defined by the walls of a corridor and the floor or roof above the corridor, a continuous gas-detection system shall be provided where piping is located and in the corridor. EXCEPTION: A continuous gas-detection system is not required for occasional transverse crossings of the corridors by supply piping which is enclosed in a ferrous pipe or tube for the width of the corridor. 5101.10.4.3 Gas-detection system operation 5101.10.4.3.1 Monitoring. The continuous gas-detection system shall be capable of monitoring the location where gas detection is required at or below the permissible exposure limit (PEL) or ceiling limit of the gas for which detection is provided. For flammable gases, the monitoring detection threshold level shall be vapor concentrations in excess of 20 percent of the lower explosive limit (LEL). See also Section 8003.3.1.6. 5101.10.4.3.2 Alarms. The gas-detection system shall initiate a local alarm and transmit a signal to the emergency control station when a short-term hazard condition is detected. The alarm shall be both visual and audible and shall provide warning both inside and outside the area where the gas is detected. The audible alarm shall be distinct from all other alarms. 5101.10.4.3.3 Shut off of gas supply. The gas-detection system shall automatically close the shutoff valve at the source on gas supply piping and tubing related to the system being monitored for which gas is detected when a short-term hazard condition is detected. Automatic closure of shutoff valves shall be in accordance with the following: EXCEPTION: When the gas-detection sampling point initiating the gas-detection system alarm is at a use location or within a gas valve enclosure of a branch line downstream of a piping distribution manifold, the shutoff valve in the gas valve enclosure for the branch line located in the piping distribution manifold enclosure shall automatically close. 1. When the gas-detection sampling point initiating the gas detection system alarm is within a gas cabinet or exhausted enclosure, the shutoff valve in the gas cabinet or exhausted enclosure for the specific gas detected shall automatically close. 2. When the gas detection sampling point initiating the gas detection system alarm is within a room and compressed gas containers are not in gas cabinets or exhausted enclosures, the shutoff valves on all gas lines for the specific gas detected shall automatically close. 3. When the gas-detection sampling point initiating the gas detection system alarm is within a piping distribution manifold enclosure, the shutoff valve for the compressed gas container of specific gas detected supplying the manifold shall automatically close.