Hydrogen-fired boiler explosion

An explosion occurred at a hydrogen boiler of a chemical manufacturing plant producing hydrogen gas and other substances.

A potential flow restriction in the feed line to a hydrogen-fired boiler was identified and specialist contractors were engaged to check it.
To this purpose, the boiler was shut down and the feed line purged with nitrogen. After checking for residual hydrogen, the line was isolated prior to examination.
After completing the line examination, de-isolation started, and hydrogen was introduced into the line.
Soon after the last isolation valve was opened, there was an explosion in the combustion chamber of the boiler, which ruptured its shell at the designed failure point.
The boiler and adjacent cooling tower pipework sustained significant damage but no one was injured.

The INITIATING CAUSE was the formation and explosion of an air-hydrogen atmosphere in the hydrogen boiler, following maintenance work,

The ROOT CAUSE in management shortcomings. This conclusion is based on the finding of the investigation:
(1) The burner management system, which allows the safe control of the combustion process, was apparently not operating when the injection of hydrogen restarted.
(2) Two safety valves in the hydrogen feed line, which forms part of the burner management system, had been manually overridden. These valves remained open during feed line checks and up to the explosion, despite other line isolations being in place.
Additional contributing factors were related to the plant operator - contractor relationship:
(3) Contractor management was inadequate. The operator placed too much reliance on the contractor’s expertise.
(4) There was no formal handover from maintenance to operations.
(5) The critical importance of the burner management system was not fully recognised.
(6) There was no risk assessment or documented process regarding the manual opening of the two safety valves that formed part of the burner management system.
(7) The job safety analysis used by the contractor was generic and the permit issuer did not examine the JSA prepared by the contractor.
(8) The section of the work permit requiring the permit issuer to state if the equipment was available for use had not been completed prior to the introduction of hydrogen into the system.
(9) The permit issuer had not received formal training in the plant and equipment covered by the permit.

boiler

The explosion happened at the restart of operations after repair works

No injuryor environmental impact.
Boiler and adjacent eqipment sgificant damage, costs unknown

Contractors’ management and supervision are critical aspects of the safety management of a plant. Because of the difference in knowledge, competence and working methods existing between plant operator and contractors, it is essential to ensure agreement on working procedures and appointment of responsibility before contractors’ work start.
The inspecting authority requested the following Actions:
Note: The source of ignition of the hydrogen-air mixture was not established. Regardless, in the absence of suitable safety controls, ignition sources in the presence of fuel-air mixtures pose a significant explosion risk.

(1) Engineering controls - Where engineered safety-critical controls have been installed, there should be robust systems to safely manage the bypassing or modification of such controls.
(2) Work permits and handover- The permit issuer and holders need to adequately understand the plant and equipment covered by a permit. Handover documentation should be confirmed as complete before recommissioning plant and equipment. A formal start-up procedure or checklist will facilitate the safe recommissioning of plant and equipment.
(3) Risk management - Permit issuers should review any associated risk assessments, including those prepared by third parties. In particular, risk assessments need to adequately address hazards.
(4) Training - Anyone who may be involved with safety-critical controls need to be suitably trained and understand the importance of these controls to the safe operation of the plant and equipment.
(5) Leadership and responsibilities - Safety obligations exist and need to be understood by facility operators, contractors and other relevant personnel before engaging in activities involving dangerous goods. Clear leadership and accountability need to be exercised, with assigned responsibilities being understood and discharged.