Historically, atmospheric hazards have been the leading cause of worker deaths in confined spaces therefore testing the atmosphere prior to entry has always been a priority. When teaching confined space entry classes, I always told the students that if they only took away one piece of information from my class, it should be that NO confined space should EVER be entered unless the atmosphere had been tested with a properly calibrated gas monitor!
The OSHA Permit Required Confined Space Standard 1910.146 indicates that confined spaces must be tested, with a calibrated direct-reading instrument, for oxygen content, for flammable gases and vapors, and for potential toxic air contaminants prior to entry. For spaces where ventilation is used to control the atmospheric hazard, then periodic testing is also needed to insure that a safe atmosphere is maintained.
The 1910.146 standard, like most OSHA standards, is performance based and not particularly prescriptive about gas monitoring requirements. The standard refers to Appendix B which provides some very basic information about the order of gas monitoring and indicates that testing should take place every four feet in the direction of travel and side to side. The OSHA Standard does not provide information on selection or calibration. It does not have a recordkeeping requirement or bump testing to verify that the gas monitor is working properly. There are a number of best practices for gas monitoring that are not specifically addressed in the OSHA standard.
NFPA is developing a best practices document for confined spaces that will include more prescriptive information about gas monitoring. Items that may be included in the document are the type of calibration gas to be used, the recommended frequency of calibration, instrument response times and bump testing and verification.
What other details should be included in the gas monitoring chapter of a best practices document for confined space entry? We would love to hear from you!