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What happened?
Technicians were investigating the shut-down of a gas-fired heating, ventilation, and air conditioning unit (HVAC).
During testing, they established the burner management controller needed replacement parts.
A second team were sent with these parts to reset the system.
When testing the automatic ignition sequence, it failed twice before lighting on the third cycle.
A technician opened the inspection and relief door to check flame stability.
Deflagration occurred within 15 seconds, allowing fire and pressure to exit through the inspection door.
Technician received second degree burns to their head, neck, and wrist.
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Why did it happen?
Injured person positioned himself in the line of fire to verify flame stability.
After manual reset, the system automatically went through a purge, fan and logic permissive for pilot and main burner.
- In-service purge timer was on a 7 second cycle, but the unit required a 90 second purge.
Technicians could not clearly see the area they needed to inspect without opening the HVAC unit:
- Burner assembly had a peephole for inspection, but it was difficult to access.
- Inspection glass on an HVAC unit did not provide clear visibility.
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What did they learn?
Auxiliary utility equipment poses high risks to personnel.
- Ensure all involved personnel are competent to operate and perform maintenance on this type of equipment.
Check all workers are aware of the hazards of removing system components (i.e. view ports) and working with open units.
- They would position themselves in the line of fire.
Utilise management of change (MOC) process to confirm the mechanical integrity of equipment.
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Ask yourself or your crew
How could this incident be prevented?
Does the system require a longer purge on start up than when in service? Why?
- How can you ensure that the automatic purge (following manual reset) allows sufficient time for the system purge?
How would you have checked flame stability in the same conditions?
What should you do if the view ports do not offer clear visibility / have been removed deliberately?
What is our emergency procedure if something like this happens here?
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Published on 14/01/21
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During start up of a fuel gas-fired heating, ventilation, and air conditioning unit (HVAC), a deflagration occurred. A technician received second degree burns to head, neck, and wrist.
