Fireplace explosion in Vancouver residential tower

Location: Vancouver

Regulated industry sector: Gas - Natural gas system

Impact

Injury

Qty injuries: 1

Injury description: Small laceration to face

Injury rating: Minor

Damage

Damage description: Fireplace glass completely shattered

Damage rating: Moderate

Incident rating: Moderate

Incident overview

A fireplace explosion in a residential tower completely shattered the fireplace glass and caused a minor facial injury to one person.

Investigation Conclusions

Site, system and components

Gas System

-From the meter a natural gas supply of 2psi is connected to each suite in a residential tower via a black iron piping system.

-Suite fireplaces are connected to the black iron pipe via soft copper tubing.

-A regulator is installed within the fireplace cavity which reduces the gas pressure from 2psi to less than ½ psi. This is the inlet pressure provided to the fireplace gas valve.

Montigo Fireplace

-The montigo 38DVM is a 20,000 BTUH natural draft, direct-vent fireplace that has a log set and ceramic glass door.

-It incorporates a gas valve, standing pilot, mercury safety switch, thermopile generator and a manual spark ignitor.

-The mercury safety switch is a device that proves the presence of a pilot flame and immediately closes the gas valve in the event of a flame loss. This prevents unburned gas from building up in the fireplace combustion chamber.

-The pilot flame heats a mercury filled tube connected to a switch. As the mercury heats, it expands and closes the switch, allowing the pilot gas valve to remain open.

-The heat applied to the thermopile generator creates a millivolt

electrical supply to the main gas valve, which in turn opens the gas valve and supplies gas to the main burner.

-The fireplace has a front and rear burner, which are lit by the pilot flame.

-The front burner is lit via a carry-over port that connects the front burner to the pilot flame.

-In order for the two main burners (front and rear) to light reliably on a call for heat the pilot assembly must be situated so that that the pilot flame will ignite the main burners without delay. This prevents a buildup of gas in the combustion chamber.

-The exhaust gasses are removed to the outside via a natural draft metallic vent.

Modified Montigo Fireplace

-The Montigo 38DVM fireplace in question had recently been outfitted with a new gas valve and pilot assembly that have different operational characteristics than those of the original design.

-This pilot assembly incorporates a quick-dropout thermocouple that closes the gas valve within seconds in the event of pilot flame loss. The quick drop- out thermocouple performs a similar function to a mercury safety switch.

Note: It is common for this era of fireplace to incorporate a mercury safety switch. However, due to the banning of mercury switches, finding replacement parts is difficult. In many cases the mercury safety switches have been by-passed, creating unsafe operational characteristics by disabling the flame proving device that prevents the gas valve from opening without a proven pilot flame. A new gas valve and pilot assembly are sometimes installed as a retrofit kit. It is important to note that, unless the retrofit has been approved by the certification agency that originally certified the fireplace, installing it will void the certification of the fireplace.

Failure scenario(s)

-A replacement gas valve and pilot assembly was installed by an unqualified technician employed by a licensed gas contractor.

-The unqualified technician was supervised by a qualified gasfitter

-The unqualified technician failed to secure the pilot assembly to the burner so that it would light the front burner reliably and without delay.

-The fireplace was energized by the resident of the suite but the misaligned pilot assembly lit the rear burner but failed to light the front burner.

-The unlit front burner emitted unburned gas into the combustion chamber, where it found a source of ignition at the pilot or main burner flame resulting in an explosion that shattered the fireplace glass

Facts and evidence

-The pilot assembly was not secured to the burner

-The pilot assembly was not positioned in a way that would reliably light the carry-over port to the front burner.

-Witness statements confirm that the fireplace was turned on and a flame was visible before the explosion occurred.

-Statement of attending Fortis technician corroborated that the pilot assembly was out of place and not secured.

Causes and contributing factors

It is likely that the incorrect installation of the pilot assembly prevented the front burner from lighting without delay, leading to an accumulation of gas within the combustion chamber, which ignited and caused an explosion.

A plugged or dirty carry-over port may have contributed to the delayed front burner ignition.

The gas valve/pilot assembly is not certified as a replacement part for the fireplace. The certification of the fireplace was voided as a result of installing the new gas valve and pilot assembly.

The technician who installed the gas valve/pilot assembly was not a qualified gasfitter. The supervising gasfitter responsible for overseeing the work performed by the unqualified technician did not adequately inspect the work.

 

Photo 1: Fireplace

 

Photo 2: Fireplace cavity

Photo 3: Fireplace pilot assembly

 

Photo 4: Exemplar pilot assembly (same model as failed fireplace but not modified)