Explosion of a spectrometer in a laboratory

[Note of HIAD event validator: this HIAD event merges two events reported in the US database H2TOOLS. The core description of the two events is almost identical, although the dates of their occurrences are approximately 1 year apart. The causes, the lessons learnt, and the consequences were the same. Therefore, it was decided to treat the two cases as one event. In the References section refences to both cases is provided.]

An explosion occurred at an analytical lab. Part of the lab instrumentation was a Furier-Transformed Infra-Red (FTIR) Spectrometer, compressed gas cylinders and supplies, and an unspecified experimental apparatus.
To facilitate reconfiguration of this apparatus, a lab operator installed "quick-disconnect" fittings on flexible tubing connected to the pressure regulators of the gas cylinders. He also fitted all equipment that needed gas with complementary "quick-disconnect" fittings.
The day of the incident, the FTIR spectrometer was heating up had to be purged with nitrogen to remove residual carbon dioxide and water vapor. Instead of connecting to the spectrometer the cylinder with pure nitrogen, the operator mistakenly connected a 10% nitrogen - 90% hydrogen cylinder. As soon as the gas started flowing into the spectrometer, the instrument exploded and was destroyed.
Only minor damage was done to the laboratory and there were no injuries.

The INITATING CAUSE was the erroneous connection of hydrogen cylinder instead of nitrogen one to a spectrometer. The operator was an expert in the use of the lab instruments and quite knowledgeable of the hazards associated with the use of flammable gases. Nevertheless, the operator failed to recognise that mistake in the choice of the cylinder to be connected.

A component of the ROOT CAUSE relates to a human mistake. However, the final ROOT CAUSE is related to failing of procedures and safety measures able to prevent the confusion of cylinders. The modification introduced to the lab gas supply system, by using fit flexible hoses which could be universally connected to all connections, amplified further the hazards and risks of the experiments.

The equipment loss summed up to $6,000

The most general lesson provided by this event, is that it is not wise to rely only on the know-how and the expertise of operators. When there is a non-negligible risk of human error, automatic, failure-proof safeguards must be installed. Relying only on the continuous attention of one operator means amplifying the probability of an incident. A procedure base only a requirement such as “Verify carefully the gas cylinder connected before starting experiments” is definitively not enough.

A second lesson is the quick connections, universally applicable to all gas cylinders and equipment, must, as a matter of principle, be avoided. Anyhow, modification to laboratory set up may introduce new hazards, and these must be considered in a new risk assessment and in a new safety design, adopting, when necessary, new preventive and mitigating measures.

The "quick-disconnect" fittings were installed to facilitate (and speed up) the preparatory steps. However, accelerating a hazardous action is not definitively increasing its safety level. Quick connections should be avoided under these conditions. If absolutely needed, they should be designed to avoid as far a possible cylinder connection confusion, for example with different fittings for different gases, not exchangeable and clearly and visibly differently labelled.

1. Procedures for safe handling of compressed gas cylinders, marking design of gas cylinders and connecting lines, and arrangement of cylinders were reviewed and modified as necessary.
2. The affected laboratory area was taken out of service.
Additional conspicuous markings were added to flammable gas cylinders and connecting lines. All hydrogen lines and valve connections were color-coded red.
3. Specific training on safe handling of compressed gases was provided for all compressed gas users.
4. The FTIR spectrometer was physically moved to a different laboratory where hydrogen cylinders were not used.