A laboratory research technician entered a lab to begin preparing samples that were to ultimately be purged in an anaerobic chamber (glove box) located in that room. As the technician walked into the lab, she looked at the chamber to see if it was adequately inflated. This chamber is equipped with a gas concentration meter, capable of simultaneously displaying the oxygen and hydrogen concentrations of the chamber atmosphere. Under normal operating conditions, the atmosphere inside the chamber is comprised of 0% oxygen (as intended/desired for an anaerobic atmosphere), approximately 2-3% hydrogen, and with the remaining balance being nitrogen (approximately 98-97%). Under such normal operating conditions, the hydrogen concentration inside the chamber is less than the lower explosive limit (LEL) of hydrogen to prevent an explosion in case air or oxygen were ever inadvertently introduced into the chamber. When the technician observed the meter's digital readouts, the oxygen concentration in the chamber was still 0% but the hydrogen concentration was at 43%. (The explosive range of hydrogen in air is 4% to 75%) An alarm light was also flashing on the meter, but an audible alarm was not heard. (At first, the technician turned the meter off and back on again believing something was wrong with the meter. She then checked the placarding of the compressed gas cylinders that were hooked up to the chamber manifold system and discovered that one of the cylinders was a mixture of 95% hydrogen and 5% nitrogen, instead of the 5% hydrogen and 95% nitrogen cylinder that was supposed to be there and immediately summoned assistance. The face of the manifold onto which the erroneous cylinder was connected is labeled as "5% H2/95% N2". The cylinder was last changed out 30 days prior to the incident, by the facility's maintenance personnel. And equipment user log indicates that the chamber had been used a couple of times since the cylinder change-out. In addition to the manifold labeling, there are also job aid instructions posted in the work area pertaining to the operation of the chamber by the laboratory researchers.
Evidence is present to show that the research staff actually requested a mixture 5% H2 and 95% N2 through the onsite acquisition system, but the vendor failed to supply the customer with the requested mixture; instead, a mixture of 95% H2 and 5% N2 was supplied. The investigation team determined that a mixture of 95% H2 and 5% N2 would have never been in the facility (for maintenance staff and end users to select from) had the vendor error not occurred.
- Ventilation System
- Glove Box/Fume Hood
Personnel should be aware that items requiring special receiving inspections should still be verified/examined by the end user prior to use.
Given that the anaerobic chamber and associated nearby electrical equipment were not designed or expected to handle a potentially explosive atmosphere, nearly all conditions necessary to have a much more serious event were present if the problem had not been discovered and the bag was not successfully purged of the hydrogen mixture.
Hydrogen use in anaerobic chambers is discussed in the Lessons Learned Corner on this website.