Explosion at a hydrogen storage of a research facility

An explosion took place at a research facility of a university, due to an accidental release of hydrogen. Hydrogen gas was used in research reactors to deposit amorphous silicon thin films. The release occurred during the replacement of a hydrogen cylinder stored in a gas cabinet. The cabinet was used to store and supply hydrogen and other hazardous gases to an enclosed reactor in an adjacent room. During the replacement of the compressed hydrogen cylinder, a quantity of hydrogen at a pressure of more than 1100 psi (75 bar) was accidentally released through a line used for vacuum purging. The explosion occurred when a vacuum bellows burst releasing the gas into the reactor enclosure. The Plexiglas walls of the reactor enclosure blew outward causing extensive damage to the laboratory. No one was in the room at the time of the incident, and no one was injured.

The INITIATING CAUSE was the erroneous release of high-pressure hydrogen into a vacuum system not rated for this amount of pressure.
This was triggered by the error of an operator who opened a valve in the wrong sequence

The ROOT CAUSE was related to the absence of a formal policy for the systematic oversight of gas handling and safety systems, together with a poor ga handling design.

valve

The explosion occurred during the replacement of a hydrogen cylinder which was stored in a ventilated gas cabinet equipped with sprinklers.

The Plexiglas walls of the reactor enclosure blew outward causing extensive damage to the laboratory.
No one was in the room at the time of the incident and no one was injured.

According to the investigation report, the incident was caused by the absence of a formal and regular review of the administrative, engineering and personnel programs associated with the compressed gas systems. Usually, a root cause is accompanied by contributing factors. These are as causal elements which did not necessarily directly result in the incident, but presented conditions in which the incident could occur. In this incident, the following contributing could be identified:
(1) The human error at the start of the sequence of events.
(2) A non-optimal design of the gas handling system, which, for example, was missing an excess flow valve and was not equipped with measures preventing mis-operations.
(3) The absence of a written procedure or checklists for purging, cylinder changing, startup or shutdown of gas system or reactor.
(4) A lack of formal training and testing programs for gas system operators.

The most important improvement required at organizational level are:
(A). Establishment of policies to ensure the continuing surveillance of maintenance operations and review of the condition of all components in the gas handling train.
(B) Routine re-evaluation of the equipment and procedures should be conducted in light of the latest advances in administrative, engineering and personnel programs.

In the aftermath of this incident, a number of technical modifications were made to the gas handling system (see Paul Moskowitz et al. in the reference):
(1) Flow restricting orifices are required for all gas cylinders. The sizes and pressures of the cylinders are limited to ensure that the low-pressure line and all components are able to withstand the pressure in the case of a catastrophic regulator failure, provided the new excess flow valve functions properly.
(2) New tied-seat regulators were installed. These regulators allow the cylinders to be purged through the regulator so that vacuum purge lines could be moved to the low pressure side of the regulator.
(3) Isolation valves were installed on the high pressure side of the regulator.
(4) Each hazard class of gas is stored in separate gas cabinets with dedicated purge cylinders.

Two critical features in place before the accident, were upgraded:
(5) Interlock of the building fire alarm system and automatic gas flow shut off circuits with online monitoring for hydride gases and hydrogen in the laboratories, gas cabinets, and reactor enclosures.
(6) Interlock circuits to ensure that all hazardous gas flows shut off automatically in the event of a loss of ventilation, gas detection, power loss, emergency shut-off buttons