Explosion in Coating Spray Equipment
An explosion occurred in the Heat Treatment Shop of this site. The explosion was centered in the electrical control panel of the High Velocity Oxy Fuel (HVOF) thermal spraying equipment. The violent explosion propelled shrapnel, killing one person present. Four further personnel were injured.
Event Date
April 24, 1998
Record Quality Indicator
Region / Country
Event Initiating System
Classification of the Physical Effects
Nature of the Consequences
Cause Comments
According to the investigation, the hydrogen, having leaked from the loose connections on the flashback arrestor of the unit, migrated into the upper compartment of the HVOF console. An explosion then occurred when it was ignited by a spark from any one of the electrical switches or relays contained there. The leaking connection was on a component which in all probability had only just been replaced. It is probable that the new arrestor, tightened the connections by hand and intended to tighten them with a spanner later but forgot to do so.
Facility Information
Application Type
Application
Specific Application Supply Chain Stage
Components Involved
High Velocity Oxy Fuel (HVOF) spray machine.
Storage/Process Medium
Location Type
Location description
Industrial Area
Operational Condition
Pre-event Summary
A high velocity oxy-fuel spray machine (HVOF) is a thermal spray processes using a mixture of a gaseous fuel and oxygen. The gas can be hydrogen, methane, propane, propylene, acetylene, natural gas, etc. The mixture is fed into a combustion chamber, where it is ignited and combusted continuously. The resultant hot gas at a pressure close to 1 MPa emanates through a convergingdiverging nozzle and travels through a straight section.Under normal operation, the upper compartment of the HVOF console would have been supplied with purge air and any holes in the central dividing panel would have been sealed by the presence of valves and other components. The purge air was not connected. Under normal circumstances, the lack of purge air pressure and open door would prevent the unit from operating. However, these two safety devices were observed to have been bypassed.
Consequences
Number of Injured Persons
2
Lessons Learned
Lessons Learned
Conclusions of the investigation:1.The hydrogen pipework had not been leak tested prior to recommissioning. 2.Safety systems to prevent flammable gas ingress into the electrical cabinet had been disconnected or bypassed.
Event Nature
Emergency Action
Unknown
Release Type
Release Substance
Ignition Source
Detonation
No
Deflagration
No
High Pressure Explosion
No
High Voltage Explosion
No
Source Category
References
References
Event description provided by HSE, original source confidential