Derek Lidstrom
At 7:20 PM on February 25th of 2023, the lower and upper floors, attic, and roof of the quaint Montecito Fire Department Station 2 caught fire. This occurred while the firefighters hung out on a quiet Saturday night.
Without warning or fanfare, a fire started at the base of the outside wall of the stucco chimney chase, 2 feet behind the metal fireplace. It raced up the wall to the attic within minutes of starting.
Around this time the firefighters inside smelled smoke and commenced searching for the source. Someone went outside and discovered the chimney fire. The crew of station #2 instantly threw themselves into action and began controlling the fire. Crews from four other fire districts eventually helped put out the fire.
Talk later over s’mores was probably of the similar nature of this fire to a number of other recent ‘mysterious fires’. All the fires inexplicably started in the framed wall, behind the back wall of the actively burning, perfectly intact, pre-fab fireplace …. For no apparent reason.
But there was a reason. Five in fact.
#1: A very attractive Bishops Arch style shroud of the ‘non-listed variety’ – (shroud should be UL listed and have a visible UL labeled and made to its UL spec’s, rerouted smoke into inside of chase cavity)
#2 No ‘Vented Chase Pan’ with a 20 yr old Superior wood burning 8 DM chimney pipe inside. (Pan should sit on 1″ tall spacers that go between top of chase and bottom of pan, pan also req’d to be 1″ wider than chase top, bottom of 1″ wide side space to be screened – which allows interior heat build-up to vent to the exterior unimpeded)
#3 There was less than 12″ of pipe, separating the pan and termination cap. (There should have been at least 12″ of pipe under term cap)
#4 The shroud had no screen. (The shroud should have had 1/2″ screen over all openings)
#5 The shroud was undersized, 28 w x 28 l x 28 h without 3″ side leg gaps. (The shroud needed to be at least 34 w x 34 l and 34 tall, with 3″ side leg gaps)
The undersized shroud in effect, temporarily staged the 600 degree flue gases from the fire inside the shroud, where the open end of the double wall flue cooling system is. The double wall, air cooled, chimney pipe then had no choice but to pull hot gases down its side (instead of cool fresh air) to try and cool itself. Without the spacers under pan the heat was trapped.
How a Factory Built, Double Wall Chimney Works
When a fire starts and hot smoke rises up the inside pipe, a current of air is hydrosiphoned down one side of the outer wall pipe. When the air gets to the bottom it makes a 180 degree turn and it leaks a little extra air or smoke – then goes up and out the other side of the pipe.
With fresh air, this system works fine. But when smoke is contained in the shroud, it is also pulled down the pipe, it leaks at each outer pipe connection – which are not air tight – and smoke quickly fills the chimney cavity for the duration of the fire. The heat leakage is worse at the bottom due to the 90 degree turn. Which is why most fires start at the bottom, behind the firebox of the fireplace. The smoke causes pyrolysis (a chemical change in wood induced by heat) to the framed chase and the entire inside of the chase gets turned into charcoal.
Exacerbating this situation was the lack of a vented chase pan. The metal chase pan was not sitting on 1 1/2″ spacers, so the interior of the chase had no chance to dispel any of the smoke / build up, and transfer fresh air back in its place.
FYI – The factory built Fireplace and Chimney Manu’s added the spacer requirement very quietly to their fireplace instructions around 1985 via an addendum, so quietly in fact that practically no fireplace dealer in the US ever bothered to start installing them. Perhaps because all wood pre-fab fireplaces dating back to 1956 needed this little elevated / vented chase pan detail and a recall would have killed the industry?
Well it took less than 20 years of having fires in this particular firehouse for the chimney and roof to catch fire. Since the chase was suffering severe pyrolysis from top to bottom, it made this fire lightning fast. Most fires of this sort start in the middle of the night, sound like a jet airplane is landing in the attic, then fire starts falling through the ceiling.
Montecito Fire Marshal Aaron Briner was at a loss for words. It was his job to enforce the Int fire Code 603.6.3 that calls for the removal of all non-listed shrouds, which he admitted to me “he did not know existed” and then he expressed skepticism that a fire code could even be retroactive. Fire Marshal Briner is likely not the only Fire Marshall unaware of this Code. But what is certain is Fire Marshall Briner would have prevented this fire in his own firehouse if he had enforced the Fire Code 603.6.3
And maybe a lot more all over town.
For the Record: It is the Fire Marshalls job to inspect all multi-family dwellings and commercial buildings annually, and enforce all new and existing Int Fire Codes. Hopefully he will be taking his duties to a higher level. Fires from ‘non-listed shrouds’ on ‘non-vented chase pans’ occur more frequently in the Santa Barbara area than anywhere else in the US.
Rob Struble, the longtime wood products manager for Heatilator Fireplaces, was fond of saying, “It is not a question of if, just a question of when a shroud will start a fire.”
To see for yourself, google ‘Santa Barbara, chimney fire, news, 2022 / 2023’. You can see the fires, the shrouds, the chase pans with no ‘air gap to house’, and you can see our firefighters saying -‘ Another mysterious chimney fire is under investigation’.
How about if our beloved firefighters instead said, “Investigation over, it’s go time!”
Derek Lidstrom attended college in Santa Barbara and has been investigating pre fab chimney fires for 31 years.
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Really interesting info, thank you.