LESSONS LEARNED
Title: Fire on Rooftop Air Conditioner/Heater Unit
Date: May 10, 2001
Identifier: 2001-NV-NTSLLNL-001
Lessons Learned Statement: Ensure annual maintenance is performed as recommended by the manufacturer for continued safe operations.
Discussion: An employee observed a strong burning odor inside his work area. Upon investigation, he discovered ash residue on the floor directly under an air conditioner/heater vent from the ceiling. Since there was no sign of smoke, the employee reported the finding to his management. Maintenance personnel shut down the air conditioner/heater unit at the disconnect switch, then lock out-tag out was applied.
Analysis: Maintenance personnel called to investigate the cause discovered the heat strips were still energized although there was no airflow from the unit. The energized heat strips caused the insulation in the unit to smolder. After reporting the cause to management, the employee was directed to shut off similar heating units in the Area 27 facilities. The NTS Fire Department and Emergency Services were called to survey and secure the situation. Sheet metal craftsmen were called to survey the insulation damage. The craftsmen installed a blank cover over the location where the heat strips were removed to prevent recurrence. The heat strip failure was due to a faulty connection on the built-in-airflow switch. The wiring at the connection fused together and the switch stayed in the energized position even when there was no airflow through the system. This caused the heat sensor and flow switch sensor (fail safe systems) not to function properly.
Recommended Actions: Develop new or edit existing maintenance procedures to incorporate an annual maintenance inspection schedule for facility blast coil heater/air conditioner units of this type and include a checklist that incorporates manufacturer recommendations.
Priority Descriptor: Blue
Work Function: Maintenance - HVAC
Hazard: Electrical
ISM Core Function: Analyze Hazards
Originator: Jerry Hawe, 702-295-6325
Contact: Terry Butler; 702-295-0278; Fax: 702-295-3643; e-mail: butler22@llnl.gov
ADC: Patricia Nolan Bodin
Reviewing Official: Patricia Nolan Bodin
Key Words: Electrical, Fire Protection, Operations
References: N/A