All of the MRC cleanroom facilities are protected by a fast response smoke detection system (AnaLASER System manufactured by Fenwal). This system continuously draws air through a piping network to the detection chamber. The piping network is located behind air returns and at the ceiling level, where there are no returns available. This system will detect highly diluted smoke & overheat by-products. AnaLASER has been proven to detect the plasticizers commonly released from wiring in the early phases of heat buildup, so even small scale soldering may not be performed in the cleanroom. Because of the level of sensitivity, it is critical that tools (especially those in chases) be monitored frequently and problems be taken care of immediately.
Activation of the fire alarm system (horns and strobes) requires immediate evacuation of the building.
The toxic and pyrophoric gas monitoring system in the MRC cleanrooms is a Zellweger Analytics system, which is a continuous monitoring system. Sampling points are located where hazardous gases are used. Throughout the cleanrooms are cable trays which contain the clear sampling tubing and related wires. Nothing else is to be put in these trays. Throughout the cleanrooms, there are light/horn trees which relate to this system. A detailed description of the gas monitoring system is available at the NNF web site. Below the trees are red emergency gas off (EGO) buttons. They will shut down all gas zones that are related to that area, i.e. EGO in Tylan area will shut off zone 13 only. The monitoring units are in MRC Cleanroom 107 and 240 entrances. The CM4 modules, or monitoring unit, can sample four sites of the same chemical class, but can’t differentiate between gases of that class. For example, a hydride unit can not differentiate between arsine, phosphine or silane. When choosing a sampling set point, the monitor will be calibrated to respond to the gas of greatest hazard.
Located in MRC 240 is the main computer for this system. The computer display located in the lobby is for monitoring only. Anybody can access the graphic overview of alarm & events displayed on the monitor. In the graphic overview, click on desired floor. Monitored areas in the facility are now displayed. One can now click on one of the areas, which will display the lamp tree and monitoring in that area. One can now select a specific sensor by clicking on it. A real time graph will appear for what is being sensed. The alarm & events page can provide a history of events or if it is in summary mode, the last event. When a new alarm event happens, a message will pop up on the screen. This system is designed to shutdown gas flows if unsafe levels are detected; however, plc power failure, exhaust failure, fire detection, or excess pressure on the low pressure side of the gas cylinder manifold will also shut off gas flow.
The gas monitoring system is tied into the building fire alarm system which would only activate if there is a hazardous gas event in the breathing zones.
The following presentation provides detailed information about the gas monitoring system in the laboratory:
The gas cabinets are manufactured by Spectra Gases and contain up to two process gases with an independent nitrogen purge system for both purity and safety considerations. All gas cabinets have self-closing / latching doors and a water sprinkler. Each cabinet is vented so that there is a minimum of 200 fpm across the cabinet window when it is open. Anytime the gas monitoring system shuts down a zone, each cabinet in the zone must be inspected before the gas monitoring system is reset. Each gas manifold has a Span gauge on the low pressure side. This gauge has been set for the excess pressure function of the gas monitoring system. They have been calibrated based on the gas that is to be located there; therefore a change in delivery pressure may require a change in Span gauge set points.
Cylinder changes may only be performed by trained and authorized personnel. Access to the gas storage rooms is limited to the authorized personnel only.
The high purity gas lines for the corrosive, toxic and pyrophoric gases have a concentric, coaxial structure and have been helically welded to form one continuous piece from the cabinet to the equipment. The process gas flows through the central core and the outer sheath is purged with nitrogen back to the gas cabinet. The outer jacket pressure gauge has both an audible and visual output at the process tool to indicate a drop in pressure.
No process toxic gas piping may be installed or modified without prior approval of the NNF director.