A malfunctioning boiler sent six people from a North Vancouver apartment building to hospital with carbon monoxide poisoning

A malfunctioning boiler caused carbon monoxide to build up in a North Vancouver apartment building and sent six people to hospital over the summer, according to a report from Technical Safety B.C. Released last month, the report describes the Aug. 10 incident at the 25-unit building. It does not identify the building’s location within North Vancouver, but says it is three storeys tall and was built in 1967.

The building is heated by two natural-gas boilers in a basement mechanical room. They were set to shut off automatically when outdoor temperatures rose above 65 degrees Fahrenheit (18.9 C). One boiler accurately sensed the outdoor temperature and shut down; the other did not, the report says. Instead, it cycled on and off to keep the water inside warm.

At the time of the incident, the temperature was above the summer shutdown setting, so Boiler 1 and the pump were off while Boiler 2 kept operating without system circulation. Boiler 2 ran only until the stagnant water inside it reached operating temperature, then shut off again. The short cycling increased the number of ignition attempts. When the temperature dropped below the set point overnight, Boiler 1 turned on and the pump sent cold water into Boiler 2, making it run for a longer period.

The report says delayed ignition during one of Boiler 2’s frequent attempts the night before the incident likely generated enough force to dislodge the vent from its connection to the appliance. The vent became wedged against a newly installed external low-water cutoff, leaving the boiler’s vent outlet open to the mechanical room. No safety system detected that the vent connector had come loose. The boiler continued to operate on subsequent ignition attempts, releasing flue gases into the room.

Later that night, as the temperature fell, Boiler 2 again ran for an extended period. The disconnected vent allowed flue gases to spill into the mechanical room. Combustion by the boiler and recirculation of those gases reduced the oxygen available for combustion, causing incomplete combustion and a significant increase in carbon monoxide production. The report says the gas entered the upper floors through holes and gaps in the basement ceiling.

There were no carbon monoxide alarms in the building, the report says. Residents did not realize what was happening until morning, when several began showing symptoms of poisoning. One occupant’s family members began experiencing severe symptoms around 6 a.m. The occupant researched the symptoms online, identified carbon monoxide exposure as a possible cause and called 911 around 11 a.m. The occupant also notified the building manager’s family, who were in a neighbouring suite.

Paramedics were dispatched, and six people were taken to hospital. Their symptoms included light-headedness, lethargy, loss of consciousness, headaches, nausea and vomiting, according to the report, which classified the incident as “major.” The building was evacuated, and emergency responders shut down the boilers with help from a technician from the responding gas utility. At the time of evacuation, carbon monoxide readings in some areas exceeded the instrument’s maximum display of 1,500 parts per million.