Hazma t IQ – Flame Impingement – A Source of CO?

Hazmat IQ Flame Impingement - A Source Of CO?

BY STUART WEST, TORONTO FIRE FIGHTER, STATION 145-B

One summer day, early on in my career as a Toronto Fire Fighter, my crew and I were handing out information for our annual Alarm for Life Campaign. As my partner and I moved to the next house and approached the door, we could hear the distinct sound of a smoke or CO alarm going off. After knocking a few times it seemed that nobody was home, until suddenly, a woman came running up the driveway. She was quite concerned that something was wrong, as why else would fire fighters be knocking at her door? We assured her that we were just handing out fire safety information, but that we could also hear what sounded like an alarm going off inside her home. She invited us inside and we quickly realized that it was her CO alarm going off, which necessitated a quick sprint back to the truck to retrieve the CO detector. The CO levels were over 100ppm and after investigating, we came to find out that she had been boiling tomatoes on a gas range stove in the basement. The pot was quite large and had seemingly smothered the flame, preventing the proper ratio of fuel to air, resulting in a buildup of CO in her home. Since that experience, I have become a Hazmat Technician and also a Civilian Gas Technician. In my training, I have come to learn that what took place that day is known as Flame Impingement.

As fire fighters, we are keenly aware of the dangers of Carbon Monoxide poisoning. At the same time, we are also very familiar with what the common sources of Carbon Monoxide are in residential settings. However, some may not be aware that an object, simply impinging on a flame can also cause incomplete combustion, resulting in the production of Carbon Monoxide. How does flame impingement cause the production of Carbon Monoxide? In the case of gas appliances in our homes, it is critical that excess air be permitted to access the combustion zone to prevent incomplete combustion. When an object impinges upon the flame, that excess air is prevented from participating in the combustion process, and without a proper amount of air to balance with the fuel, the result is incomplete combustion and the production of Carbon Monoxide. Another common example of flame impingement that occurs commonly in residential settings are gas fireplaces. When your Gas Technician commissions the appliance for the first

time the logset will have a particular arrangement. If you’ve had someone clean the inside of the firebox and the logset was not returned to exactly the correct positions, the logs may begin to impinge on the gas flame. Signs of this will include the glass front of the fireplace becoming coated with soot in a very short order, in addition to the inside of the firebox and the vent termination on the exterior of the house.

Where flame impingement can be of particular concern, is in the case of an, unvented appliance. Examples of unvented appliances in the home are gas ranges and dryers. If the flame in your furnace was being impinged upon, it might be an annoyance, in that your system would likely be very inefficient and drive up your gas bill. However, because the products of combustion are vented to the outside in a furnace, it would likely not impact human health, unless the venting system was compromised. Although, if the flames on an unvented appliance are being impinged upon, there is nothing to prevent a buildup of Carbon Monoxide in the living space itself. Most over the range exhaust fans are not close enough to the burners nor powerful enough to exhaust all of the CO and is only present as a Building Code requirement in order to exhaust moist air from cooking activities. Typically, we do not use our gas cooktops for all that long; certainly not long enough for a household CO alarm to register a high reading. However, there are occasions where this can occur, such as in the case of the home we encountered doing our door to door Alarm for Life campaign on that hot summer day. People who have existing health conditions, like the elderly and/ or young children, are particularly susceptible to the harmful effects of CO poisoning and may not require the same cumulative dose of CO as a healthy adult to cause some serious harm.

The moral of the story here is to do a thorough investigation. All gas appliances in the home have the ability to cause CO production, so we need to look past the typical culprits, such as the furnace or hot water tank. Follow the SOG’s and the training notes, eliminate one source at a time. A faulty CO alarm should only be considered after all potential sources have been eliminated.