Gas leak in Richmond apartment causes explosion and fire
Regulated industry sector: Gas - Natural gas system
Work performed during a natural gas fireplace retrofit created a gas leak within a four-story apartment building resulting in an explosion and fire. The building was evacuated and the fire department extinguished the fire.
- Quantity of injuries: 0
- Injury description: None
- Injury rating: None
- Damage description: Damage to multiple suites in an apartment building due to an explosion, fire and fire suppression activities.
- Damage rating: Major
Incident rating: Major
Site, system and components
A four-story apartment building that has natural gas fireplaces in each suite. The building gas supply was distributed through a gas pipeline in the parkade level providing gas at 2 PSI pressure. The gas line branched to a number of vertical gas pipes (“risers”) in the parkade.
Each riser incorporated a line pressure regulator that reduced pressure to under ½ PSI. Each vertical riser provided gas to the 1st, 2nd, 3rd and 4th floor suite fireplaces. The gas supply to the riser and all four suites could be turned off using a gas shut off valve located in the parkade (Photo 1).
Each fireplace was connected to the gas riser using a narrow copper tube (commonly referred to as a “whip”) attached to a T-fitting in the riser, (Photo 2). A schematic diagram of the piping system is shown in Figure 1.
A company was contracted to replace the existing natural draft fireplace in one suite with a direct vent-type fireplace. The new fireplace required an additional duct serving as an air supply to the fireplace, which fits inside the original exhaust duct. The new direct-vent fireplace’s dimensions were larger than the existing fireplace.
Gasfitters were replacing the existing fireplace in a 2nd floor suite. They did not turn off the gas supply to the gas riser prior to doing this work.
In order to install the new 2nd floor fireplace the gas riser pipe and T-fitting were moved so the larger fireplace would fit into the hearth. This gas riser pipe extended to suites in all four floors and was attached to three other fireplaces. Moving/rotating the riser pipe at the 2nd floor suite caused the copper whips attached in the 3rd and 4th floor suites to break and allow gas to escape. Gas leaked out of the broken whips and was ignited by a fireplace pilot light in the 4th floor suite, resulting in an explosion in the 3rd and 4th floor suites.
Facts and evidence
The apartment suites involved in this incident on the 1st through 4th floors are referred to as suites #1, #2, #3 and #4, respectively.
Gas fitter #1 was replacing a natural draft type fireplace in the 2nd floor (suite #2) with a new high efficiency fireplace. The gas fitter stated that the existing copper whip was too short and brittle (due to age) and was concerned that it would kink if they had to bend it to accommodate the new fireplace. Gas fitter #1 replaced the existing copper whip with a new longer copper whip, (Photo 2 & Photo 4). Doing so with the gas supply still on meant that gas would leak out of the riser pipe during the time the original whip was disconnect and the new whip was connected, which presented a hazard.
The gas fitter stated that the location of the gas riser T-fitting blocked installation of the new fireplace (the new fireplace was larger than the original fireplace). Gas fitter #1 stated that they moved the gas riser out of the way and strapped it to an adjacent 2x4 stud. The gas riser was connected to fireplaces in four suites so moving the gas riser in one suite can affect another component in the system, as was the case in this incident where two other whips were damaged. Given that the whip in suite #2 was thought to be brittle then the other three whips may have been brittle as well and subject to damage by moving the gas riser. The effect of moving the gas riser in suite #2 on the rest of the system (e.g. whips in suites #1, #3 & #4) was not verified by the gas fitter.
Gas fitter #1 then proceeded to the roof to install a metallic liner down the existing metallic fireplace chimney vent. Gas fitter #1 requested help from gas fitter #2, who aided in dislodging and installing the vent liner.
Gas fitter #2 stated that they detected a gas odour near the vent serving the fireplaces and then a strong gas odour when they opened the roof hatch adjacent to the vent. The gas fitters called the owner of suite #2 and advised them to call the gas utility [to turn off the main gas supply to the building]. Moments later the explosion occurred.
The gas utility technician arrived on site shortly after the incident and turned off the main gas supply to the building. The technician reported to have found the gas riser isolation valve in the “on” position, that supplies gas to the four incident suites. The utility technician then turned the gas riser isolation valve off. CCTV security video confirmed that the valve for the gas riser in the parkade had not been turned off prior to the incident.
The gas fitter replacing the fireplace in suite #2 confirmed that he had not asked building management to turn off the gas supply to the riser. The building manager stated that he had not been asked by this gas fitter, or any gas fitters who had previously replaced fireplaces in other suites, to make arrangements to access suites with fireplaces attached to a common gas riser in order to turn off and relight fireplace pilot lights.
Damage analysis inside the apartment suites determined that the explosion occurred in the 3rd and 4th floor suites. It was apparent that gas leaking in the fireplace hearth of these suites had fueled the explosion. The fireplaces in these suites were found to be dislodged out of the wall as a result of the explosion. The fire investigators reported that burn patterns in the 3rd floor suite indicated that natural gas from the broken copper whip sustained the fire until the main gas supply was turned off (Photo 3).
In suite #4 the standing pilot for the fireplace was found to be in the “on” position indicating that the pilot flame was burning prior to the incident.
The copper whip in suite #1 was found cracked. In suite #3, it was found completely fractured (Photo 6) and in suite #4 the whip was found partially fractured (Photo 7). In all cases the fractures occurred where the copper whip was connected to the gas riser T-fitting.
The T-fitting in suite #1 was found pointing towards the fireplace. In suite #2, the T-fitting was found pointing away from the fireplace. In suites #3 and #4, the T-fittings were also found pointing away from the fireplace. Examination of similar suites in the building that were not involved in the incident found the T-fittings pointed towards the fireplace in all cases. This indicates that the final positions of the T-fittings found in suites #2, #3 and #4 had changed from their original positions, likely due to manipulation of the riser by gas fitters during installation of the new fireplace. Fire investigators reported finding tool marks on the T-fitting and riser pipe in suite #2.
The riser pipe was clamped to the floor assembly where it penetrated the parkade to the first floor, which could restrain movement/rotation of the T-fitting in suite #1. The riser was not clamped where it penetrated the 2nd, 3rd or 4th floors. It is possible that movement of the threaded fittings in the piping system allowed the T-fitting in suite #1 to remain stationary (as restrained by the riser clamp) while the fittings in suites #3 and #4 rotated as the T-fitting in suite #2 was rotated.
Holes in the concrete floor allow for the riser to pass through each of the four floors. The gap between the riser pipe and hole was filled with a pliable fire stop material. This material did not restrain rotation of the riser pipe given that it was not firmly adhered to the riser at the 2nd, 3rd and 4th floor levels. This material was found broken away from the pipes leaving gaps visible between the pipe and fire stopping material.
Examination of the gas line components for the four fireplaces was conducted by a metallurgical laboratory, refer to the report in Appendix A. The findings included the following:
Examination of the whips found that the tube wall of whip #1 was partially cracked, and completely cracked through the tube wall of whips #3 and #4.
Metallurgical analysis of whips #3 and #4 indicated that both whips had been exposed to a severe bending load that exceeded the mechanical strength of the copper tube resulting in complete separation of whip #3 and partial separation of whip #4.
Analysis of the copper whip in suite #3 determined that it had fractured before the explosion, rather than as a result of the explosion. The copper whip in suite #4 had also partially fractured before the explosion allowing a small amount of gas to maintain the pilot light burning until the explosion. The force of the explosion further opened the fracture in whip #4.
The copper whips broke from being bent 90 degrees and forced in a direction away from the fireplace. This was consistent with the action of turning and pushing the riser T-fitting in suite #2 in a direction away from the fireplace.
Investigators conducted tests at the apartment building and found that the new fireplace would not fit in place in suite #2 unless the riser pipe was pushed to the left and T-fitting pointed away from the new fireplace. Whereas in the undamaged suites having original fireplaces, the T-fittings pointed towards the fireplace as originally installed. This indicates that the riser pipe and T-fitting in suite #2 were moved and rotated to fit the new fireplace. In suite #3, investigators found an indentation on a wood stud caused by the T-fitting being rotated to the left with enough force to create a depression in the wood.
Moving the gas riser pipe at suite #2 also moved the T-fittings connected to fireplaces in suites #1, #3 and #4 which caused the whips in suites #3 and #4 to break because they were too short to accommodate this movement. The copper whip was not ductile enough (i.e. too brittle) to bend without breaking and hence fractured when gas riser movement forced the whips to bend 90 degrees.
Following the incident a pressure test on the gas riser confirmed that no leaks were present in the black iron riser pipe itself. This finding limits the source of the gas leak to the copper whips in suites #3 and #4. The leaking gas migrated up through the wall cavity that housed exhaust ducts for the fireplaces on all four floors. The explosive fuel mixture was present within the wall cavity of the 3rd and 4th floors when it was ignited at the 4th floor.
The regulations and codes that apply when replacing an appliance (fireplace) and gas piping (e.g., copper whip) include the Gas Safety Regulation and CSA B149.1-15 Natural Gas and Propane Installation Code.
CSA B149.1-15, clause 4.4.1 requires that careful attention must be paid to both the execution of the work and how the work may affect the arrangement of the installation. In this incident, two key aspects had required careful attention, the fact that the three attached whips could be affected by moving the gas riser in suite #2, and that these other whips may be brittle like the whip in suite #2 was assumed to be.
CSA Code B149.1-15, section 6.22 Testing of Piping, Tubing, Hose, and Fittings, requires that a pressure test be conducted before an appliance is connected. If the fireplace had been replaced and the original whip remained in place, the gas supply could be isolated by turning off the gas shut off valve attached to the whip. The pressure test would be for the new fireplace connection to the whip. The Code allows for a liquid solution (e.g., soapy water) to be used to locate a leak in this case, (a gas pipe less than 20 ft. long and under 0.5 psig).
Given that the whip was replaced, the gas supply would be isolated by turning off the gas riser isolation valve in the parkade. The gas riser isolation valve was not turned off before disconnecting the whip suite #2, which allowed gas to leak from the gas riser T-fitting, which presented a hazard. Although clause 6.22.1 of CSA Code B149.1-15 implies that the gas supply be isolated, the Code does not explicitly state that the gas supply be turned off before the whip is removed. The fireplace manufactures’ certified instructions and certified gas fitter training are expected to provide instruction on isolating gas supply for replacing a fireplace and whip.
The gas riser T-fitting in suite #2 was moved/turned during this gas fitting work which affected the entire system of whip connections on the gas riser. Therefore, the entire system should be pressure tested to check for leaks as defined by CSA Code B149.1-15. This pressure test would have been achieved using a pressure gauge installed downstream of the gas riser isolation valve in the parkade. Clause 6.22.2 of the Code requires using either air, inert gas, or carbon dioxide as the test gas. There is no provision in the Code for natural gas to be used as the test gas in this case.
Testing for leaks in the system would have provided an opportunity to detect and repair leaks (suites #3 and #4) before connecting the fireplace in suite #2 and before relighting pilot flames in all four suites.
Causes and contributing factors
The gas riser pipe was moved at the 2nd floor suite which in turn fractured copper whips supplying gas to the 3rd and 4th floor suite fireplaces. This work was conducted on an energized system which caused a gas leak in the presence of an active pilot flame in the 4th floor suite that ignited the gas resulting in a significant explosion.
A primary contributing factor was the natural gas supply valve not being turned off before disconnecting a fireplace gas line from the gas supply riser in an apartment suite.
Read the full report
For full report, including supporting images, download the PDF below.