LODD: What Are The Chances? In August 1996, a deputy chief in a New Jersey department responded to a fire in a fast food restaurant. All involved reported during the subsequent investigation that it was "just a routine fire." Per the report, the fire started in the flame broiler and spread to the fat fryer. It spread through the exhaust fan and ductwork to the roof, and upon the first engine's arrival, that it did have visible fire on the roof.

The deputy chief responded from home to the scene. He was seen outside of the building, near the back door when a large cloud of smoke from the fire banked down toward him. He was not wearing an SCBA. He later reported he inhaled some of the smoke, held his breath and walked out of the cloud. He was immediately attended to by a BLS crew on scene and rapidly transported to the hospital. At the hospital he was in severe distress, and almost needed to be placed on a ventilator. However, he improved and was discharged after two days. Ten days after the incident, he was at home when he collapsed. EMS found him to be in cardiac arrest, and efforts to resuscitate him were not successful. The medical examiner reported that the cause of death was "marked tracheobronchial inflammation, alveolar hemorrhage and pulmonary edema due to smoke inhalation containing phosgene." Phosgene? Where did that come from? Isn't phosgene some old chemical weapon?

Immediately after the incident, the department initiated an investigation into this "routine fire." What was found was that the fire spread to the roof through the exhaust ductwork above the hamburger broiler, where it was drawn into the rooftop AC unit. The automatic fire suppression had activated but was ineffective in extinguishing the fire because the grease buildup in the ductwork blocked one of the dispensing nozzles which resulted in rapid fire spread. The heat burst the cooling coils releasing Freon gas (12 lbs) into the fire that thermally decomposed into acid and phosgene gases. The toxic gases were drawn into the building and mixed with smoke and gases from the fire which vented out of the rear of the building where the chief had been standing. 

This fire fueled by grease in the hood and ductwork eventually spread to a rooftop air conditioning unit and a hose containing Freon 22 that had ruptured. (There were no devices to shut down the AC unit during fire) When this substance (chlorodifluromethane) is exposed to heat and decomposes, several substances including hydrofluoric and hydrochloric acid, chlorine gas and phosgene are produced. Phosgene is a toxic gas, considered a pulmonary irritant. Its structure includes a carbon, oxygen and two chlorine molecules. It was used in World War I as a chemical weapon.

Today, exposure can occur in the manufacture of dyes, resins, pesticides and pharmaceuticals. It is also created in the heating and combustion of chlorinated organic compounds. This is how this chemical was found on our "routine" fireground.

Phosgene is slowly dissolvable in water. This means that when it is inhaled, it does not dissolve in the mucus membranes of the airway quickly, so it can travel into the lower airways. If it was rapidly dissolvable, it would do so in the upper airways and its effects would occur there. Once it dissolves, it turns into carbon dioxide and hydrochloride acid in a process called hydrolysis. The hydrochloric acid causes inflammation and death of cells in the lower airways and the lung itself.

 Who would've though that a fire in a fast food restaurant had phosgene present? Do we even consider HVAC fires as dangerous?

HVAC in High Rises: Smoke control systems using mechanical equipment, such as fans and dampers, rely on the integrity of this equipment to control the spread of smoke within a building. Fire/life safety and HVAC systems must be carefully integrated to ensure reliability in smoke control systems. 

SMOKE CONTROL SYSTEM: A system that is used to limit the migration of smoke within a building due to a fire. There are several methods to limit this migration, and some are designed to provide a tenable environment for occupants to egress the building. A smoke control system can include physical barriers that limit smoke from migrating outside the zone, a combination of physical barriers and mechanical systems, or only mechanical systems to control the spread of smoke. This will require the assistance of building personnel familiar with the building’s systems.


During summer months, poorly serviced air conditioner units can leak and ignite. AHU's can leak onto electrical equipment short circuiting it and start a fire.

In urban areas, large heavy commercial AHU's installed on the roof pose a serious danger to unsuspecting firemen working below. A roof can be weakened due to fire, water damage, age and neglect. An air handling unit installed on a lightweight constructed roof or a recent change of occupancy can have tons of weight coming down during a roof collapse. These units are usually located on the roof, in mechanical rooms or on the ground adjacent to the property.

DUCT DETECTOR activations are one of the most common false alarms fire departments respond to. Many of these alarms are caused by dirty filters, ducts and dust accumulation on heating strips. See how they are tested below.

NEWS:Workers Cutting Torch Starts Fire at Chiller Plant Causing $300,000 in Damage- CLICK HERE

TIP:  NFPA 72- Duct smoke detectors are considered mechanical devices, not life safety devices. A duct detector is not allowed to replace an area smoke detector because if the AHU is not running, the smoke wouldn't be detected.

HVAC 2014 Dallas:A fire at an underground thermal storage tank located underneath of a high-rise parking garage killed three workers. The tank was inside of a mechanical equipment room and part of the HVAC system. CLICK HERE for story.

RESIDENTIAL HVAC's running during a fire will contribute to fire spread. Above (Right) fire, smoke and gases pulled into the attic by a functioning air handler. (Center) Fire spread in air handler compartment. (Left) First floor fire distribution by duct system and functioning air handler.

(Below) A residential and commercial AHU fire. Many of these fires are caused by improper installation of the power cables, or too many cables that chafe on the sharp edges running through the poke hole.

AHU's (Air Handling Units) are devices used to regulate and circulate air as part of an HVAC system (HVAC- Heating, Ventilation, Air Conditioning) It usually will have a blower, heating/cooling elements, filter racks or chambers and dampers in a large metal box (as seen on roof tops on large buildings). They usually connect to a duct system that distributes the conditioned air throughout the building and returns it to the unit. Some units are powered by natural gas or propane, and these hazards shouldn't be treated any different than usual. Units rated over 2000 CFM (Cubic Feet per Minute) will be provided with duct detectors, which are required to shut the unit down automatically when activated.

COOLING TOWERS in an HVAC system are used to dispose of unwanted heat from a chiller.

CHILLERS (below) are machines that remove heat and liquid via a vapor-compression or absorption refrigeration cycle. HVAC chillers are industrial and commercial grade refrigeration systems used in cooling applications. The system includes a compressor, evaporator, condenser, reservoir, thermal expansion valve and stabilization assembly. HVAC chillers use water, oil and other liquid compounds as refrigerants.

There's always a possibility that chillers located in target hazards like hospitals, government buildings and movie theatres can start arcing due to improper maintenance and installation, resulting in a fire or smoke condition throughout the building.

HVAC: Fire started in the MER with CHILLERS and chemicals on top of a parking garage in Denver. See VIDEO here.

This fire was caused by a new HVAC system installed at Johns Hopkins hospital.

AHU's (AIR HANDLING UNITS) Air handler malfunctions are rare incidents that have the potential to result in fire and smoke conditions triggering alarm activations. The air handler in an HVAC system has electrical and mechanical components in it that can experience problems from time to time such as clogged filters, faulty wiring, worn belts, fan motors and compressor issues.

HVAC systems in commercial buildings can be beneficial and assist the fire department, but also create problems for them as well. Firemen must have a basic understanding of HVAC systems. (See LODD below)

A common problem that causes unwanted alarm activations is dust accumulation on the heat strips inside the AHU when the heat is turned on, which activates the duct smoke detector. NFPA 72 now allows duct detectors to send a supervisory signal instead of an alarm signal due to frequent false alarms.

NFPA 90 A covers the construction, installation, operation, maintenance of AHU's.

Having basic knowledge of residential and commercial HVAC systems can help determine what's causing an alarm activation/smoke condition and how to shut the unit down. Smoking AHU's in commercial buildings will obviously give off a mechanical odor. Once located and confirmed to be the source, shut the unit down and notify the building representative.

Most AHU's have duct detectors. Air handler units over 2000 CFM are required to automatically shut the system down during an alarm activation. When conducting fire preplans in commercial buildings, visit the roof/penthouse area or adjacent property/attached occupancies and locate the larger air handlers, chillers, cooling towers, shutoffs etc..


FIRE DAMPERS: Prevents the spread of fire and smoke in the HVAC ducts running through fire resistive rated walls and floors.

Denver F.D operates handlines on the roof fighting an AC unit fire.

A fire at the Kansas University sports complex caused by a cooling tower.

Residential fire in Charlotte N.C. started by the HVAC in the attic.