Hi guys,
I hope someone can help

1. We plan to install a Near Infra Red analyzer in a shelter room at some user's site. The shelter room already contains many instruments and by customer's definition it is a non ex zone. The customer agrees that since the instrument itself is to be installed in a shelter - there is no need for certification for the instrument itself.

2. Optical fibers will be coming out of the shelter and via conduits will reach some measuring points in the process. The exit and entrance of the fibers out and into the shelter are insulated from outside world by the customer.

3. All flanges and connections on the sensor that is installed in the process area, which is Ex zone 1 comply with the requirements. The sensor has no electrical components of any kind. Light comes into the liquid stream which flows in the flow cell via special sapphire windows and exits the liquid via another window and into the second fiber that takes it back to the sheltered instrument.

4. The irradiance in the fibers at any time is less than 0.25 mW/square mm.

5. I would like to know what is the max allowed irradiance in optical fibers that are located in ex Zone 1.

If anyone can refer me to a proper document or actually knows what is the allowed max irradince it can be very helpful.

many thanks,

Gabi Levin
Brimrose corp.
Baltimore MD USA

 

The only reference I am aware of relating to this is in IEC61241-0, and applies to dust atmospheres rather than gases. According to this standard, for Zone 20 or 21 the irradiance must not exceed 5 mW/mm2 or 35 mW for continuous wave lasers, 0.1 mJ/mm2 for pulse lasers with pulse intervals of at least 5 s.

http://www.cdc.gov/niosh/mining/pubs/pdfs/ilsc.pdf gives some further information on lasers used to measure methane in mines and may be worth viewing.

Hope this helps,
Bruce.