The use of the proper purging system will reduce the enclosure (internal) rating from Class 2, Div 2 to a non-hazardous rating. This is only as long as the enclosure remains sealed and the appropriate amount of pressurization is applied ----continuously----AND ----for a minimum period of time. What this means is this: The enclosure, no matter what the NEMA rating, 12, 4X, etc. will be open when installed and periodically serviced or accessed for what ever purpose, in the area of which hazardous gases are present. During this period of time the enclosure MUST be de-energized, power completely removed from the enclosure. The reason....the enclosure becomes a hazardous, explosive environment. To re-energize the enclosure it must be resealed and purged with clean air for a minimum period of time (depending on the size of the enclosure and the exchange rate of the purging system). ONLY after this minimum period of time has passed under these conditions may the enclosure be re-energized. Pay particular attention to the explosive seal requirements for all conduit and cable entries. Also Interlocks and proper labeling of all enclosures is required and observance of proper lockout-tagout procedures is a must. This condition applies to all enclosures INCLUDING the chart recorder. NOTE: The chart recorder may require purging also if it is in a sealed enclosure even though mounted through the NEMA 4X enclosure. There are exceptions to this such as if the environment has been tested and proven to be free of hazardous gases during the time of service. However I prefer always to err on the side of safety. Please refer to the site I previously mentioned if only for information and education on the subject and if the chart recorder must be accessed on a daily basis, while the system is energized, it would probably be best to mount this remotely in a clean and safe environment such as a control room. I hope this helps. I am not an expert on this subject, by any means. I've just done this a dozen time or so. Please spend a few hours or a day studying this subject and talk to an expert at the link I gave you or a similar company. He or she may be able to enlighten you on the subject of the chart recorder. It will pay off in your short and long term efforts. Good Luck! Scott
