IEC 60079-29-4 Ed. 1.0 (2009-08) Explosive atmospheres – Part 29-4: Gas detectors – Performance requirements of open path detectors for flammable gases has been issued for voting as a Final Draft International Standard (FDIS) but can be bought now rather than waiting for the published standard.
This is a relatively new approach being used by IEC. Once published you will receive the definitive version. This special package allows you to save 25%
No technical changes are permitted at the FDIS stage and so you are getting a document that is very close to the final standard.
See below:
http://webstore.iec.ch/webstore/webstore.nsf/artnum/FDIS31819?opendocument&mlref=JP