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Smoke detector lag time?

Post in 'DIY and General non-hearth advice' started by bluedogz, Jul 21, 2012.

  1. bluedogz

    bluedogz Minister of Fire

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    Recently received an email from an acquaintance who suffered a house fire...

    Last Wednesday, July 11th, before seven in the morning, I was awakened by the smoke alarm. Our house was on fire and went up like a tinderbox. We had less than three minutes to get ourselves and my 88 year old mother out before the flames were through the roof and we made it out with only seconds to spare. We got out of the house in our pajamas and I didn't even have shoes. The house could not be saved. Less than 5 minutes from the time I heard the alarm the house was totally in flames.
    I am trying to figure ... is a 3- or 5-minute lag time from smoke-detector-to-fully-engulfed a normal time for a smoke detector? I know there are a bunch of firefighters on here who might have an opinion...​

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  2. jeff_t

    jeff_t Minister of Fire

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    Sorry to hear of your friend's loss. Been in enough burning buildings to know what they are going through.

    There are different types of smoke detectors http://en.m.wikipedia.org/wiki/Smoke_detector#section_2. They work differently, and each is better in different situations.

    Construction can also play a role. I've been in a couple of old balloon frame constructed houses that had heavy smoke just rolling out of the eaves, but it was perfectly clear inside. Balloon frame is open all the way to the attic, with no firestops between floors. That means there can be a fire in the basement, the main living area can be clear, and the attic can be totally involved. An electrical fire in the wall could go undetected and produce the same results.

    I've also seen smoke detectors that were all black and nasty, and even though they never went off, they worked when the test button was pushed.

    I'm not saying that smoke detectors are worthless and a waste of time. They save lives. Everybody needs them, but you need to be aware of how they work, and which ones are the best in a particular application. Your local fire department's fire prevention officer/ fire marshal is probably your best source of information. They will be more than happy to visit your home and make a recommendation.
  3. bluedogz

    bluedogz Minister of Fire

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    This just made me wonder... these people described going from "Is that the smoke alarm?" to "Holy Crap the whole house is burning" in a described 5 minutes. Considering that a pot on the stove can set off smoke alarms pretty dependably, I was trying to figure how realistic this description was, and if such a thing is a realistic risk in my own house.
  4. velvetfoot

    velvetfoot Minister of Fire

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    You've got your photoelectric and ionization type smoke alarms. Both have their pluses and minuses. I've read that some areas in the Northeast are pretty gung ho about the photo type.
  5. firefighterjake

    firefighterjake Minister of Fire

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    Ah, a topic near and dear to my heart . . . this is my forte . . . at last something I know a lot about . . . something I don't feel like an idiot about (like that danged computer.)

    In answer to the first question posted . . . yeah . . . as Jeff-T mentioned there are many factors ranging from smoke detector type (photo-electric or ionization) and what type of smoke is being produced (is it smoke from a slow, smoldering fire or a fast, flaming fire), building construction, placement of detectors, maintenance of the detectors, age of the detectors, etc. . . . but in general when you hear an alarm you should not be lying there in bed thinking your teen-age son is burning the microwave popcorn while making a late night stack.

    The National Fire Protection Association did some experiments a few years back and made them into videos -- Fire Power and . . . crap . . . cannot remember the name of the other video. In any case, in one video they built a room in a large lab, filled it with typical home furnishings for a living room and set it on fire using a heated coil to simulate a discarded cigarette in a trash basket. From first flame to where the fire literally blows out the front panes of glass is something like 3 minutes.

    In the other video which I feel is a little more realistic . . . and a little more updated as the other video has a very 1980s vintage look . . . they did a similar experiment using a two-story Colonial where they actually discard a lit cigarette into the trash or couch (I forget which) and from first flame to where the fire is breaching the window and curling up the outside of the house is 5 minutes.

    In both videos smoke detectors sounded relatively soon after the fire went to flames . . . but then . . . as now . . . we tell folks that when they hear the alarm they need to get out right away as far too many people do not realize how fast fire can increase in size.

    A few other facts . . .

    As Jeff T mentioned . . . pushing the test button on most detectors simply tests that the alarm has a power source and an audible alarm . . . it does not test the sensing unit. If you want to test the sensing unit some hardware stores sell testing smoke. That said . . . the biggest thing to bear in mind is that the biggest reason most detectors fail to activate is that they've been purposefully disabled (often due to previous false alarms) . . . which is one reason I am a big fan of detectors with hush, or silence buttons, that you can disable the audible alarm if you know there is a false alarm . . . and then the alarm will automatically reset after 5 minutes or if it detects the same or more smoke will go back into alarm mode.

    There was a bad fatal fire in . . . I think Vermont a few years back . . . the ionization detectors failed to alarm despite a good charge of smoke in the home. I remember the legislators of the state pushed for a bill to require all homes have photo-electric detectors. I have mixed feelings on this . . . personally . . . when folks ask . . . I suggest a combination of ionization and PE detectors is the best method of protection . . . and it's what I have done in my own home.

    As I mentioned the age of the detector plays a part . . . 10 years or older and you should be replacing the detectors in your home. They have a life expectancy . . . some can last longer, some may die a younger death. But in studies they have found that at about Year 10 it is best to replace them to insure the sensor is in working order.

    As always . . . when you change the clock in the Fall, change the batteries in your detectors (even the electric detectors.) The reason we suggest this time of year is for a reason . . . although some folks go with their birthday, anniversary, Christmas, etc. Starting in the Fall we start to see an increase in home heating fires that peaks in January or February . . . and as a FYI . . . you don't have to worry so much now about changing the batteries in the Spring since the tech has reached the point that usually the batteries will last a year or so with no issues.

    OK . . . I think I've written enough . . . as you can see . . . it's an important topic to me. I personally know of many people who have been saved because of that $10 piece of plastic and electronics on their ceiling . . . and sadly I have seen first hand in body recovery or investigations afterwards of the consequences of not having working smoke detectors in the home.

    Final thought . . . just one working smoke detector increases your chances of survival in a fire by 50% . . . but only if it works. About the only thing better is being in a home with a sprinkler system . . . or maybe sleeping with a firefighter . . . yeah, that pick up line never works for me. . . .
    Lewiston, heat seeker and Jags like this.
  6. stee6043

    stee6043 Minister of Fire

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    Great post, FFJake. Makes me want to run to the store and blow a bunch of money on new detectors as mine are now 9 years old. Sadly, with as many detectors as "newer" homes have these day's it's no minor investment. I believe I have 11 in my house. Just replacing the batteries every year costs more than a case of beer! ha.

    It looks like the average dual-sensor "wire-in" detector on Amazon.com is running $30 +/-. Does that sound about right to you? For me that would be a $300+ expense. Probably a great investment but I can certainly see why folks don't run out to replace them every 10 years.
  7. stee6043

    stee6043 Minister of Fire

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  8. save$

    save$ Minister of Fire

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    I tossed all my older ones and went to the new ones. My thinking was they may have improved performance. I found a unit with a ten year battery. You just toss the whole unit when it is time. While on the subject, don't forget the carbon monoxide detectors. Need to. Ck both.l
  9. firefighterjake

    firefighterjake Minister of Fire

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    Yeah . . . more features = more money vs. the $5-$10 Fire Prevention Month specials on the plain Jane battery jobs that you see advertised in October.

    If one cannot replace all the detectors at once I would suggest replacing a few each year . . . starting with the area in or near the bedrooms.
    Lewiston likes this.
  10. firefighterjake

    firefighterjake Minister of Fire

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    Voice or no voice . . . depends on whether one has young children living in the home.

    http://pediatrics.aappublications.org/content/118/4/1623.abstract

    If there are children . . . and the funds allow . . . getting a voice capable alarm seems to make sense based on what studies and reports I have come across.
  11. firefighterjake

    firefighterjake Minister of Fire

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    I have several of these myself in my home . . . 10 year lithium power cell . . . although I did find that with the first generation I think I only got 8 or 9 years out of it . . . still not a bad deal for not having to replace the batteries every year . . . plus it had the silencer/hush feature.

    And your comment reminded me . . . while smoke detectors should be replaced every 10 years the replacement time on CO detectors varies according to the manufacturer. A few years back our Inspector called around and found that it depends on the company with some manufacturers suggesting replacement in as little as 3-4 years and with some as much as 7-8 years.
  12. stee6043

    stee6043 Minister of Fire

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    I almost pulled the trigger on 10 new detectors this week. But alas, instead I spent $35 on 9V batteries. I'm glad this thread came up. Next year I will be pulling all of my detectors and replacing them. They are probably 10 years old this year...
  13. greg13

    greg13 Feeling the Heat

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    One other factor comes into play also. Unchecked, a fire will double in size every 30-60 seconds.
  14. save$

    save$ Minister of Fire

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    The date is on the back of each unit. Older units may work, but may not be giving the performance you are counting on.
  15. seige101

    seige101 Minister of Fire

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    Save$ is correct. Also remember they might only be 8 years old to you but some times they can be 1-2 years old when you purchase them.
  16. velvetfoot

    velvetfoot Minister of Fire

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    I think the last co detector I got has a built in countdown timer til end of life, and then it beeps or something.
  17. Lewiston

    Lewiston Burning Hunk

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    FF Jake thanks for the wealth of info. Didn't know about the 10 year lifespan - just ordered replacements.
  18. btuser

    btuser Minister of Fire

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    Go figure. I just put 200 bones into new detectors for the whole house. I put dual detectors at the landings and photo in the in-law (one outside a bathroom and one is in the kitchen/living room). I'm going to extend the circuit and pop some into the bedrooms (staying below the limit). I also got heat detectors for the garage and attic and another heat detector for over the boiler. I bought another heat detector for the family room thinking it may kick off if a fire ever gets out of the wood stove but I'm not sure about that. Here's a neat little video they showed us in class about how fast a fire can spread.

    From my understanding that was not a "dry" scotch pine. It needed water, but wasn't anymore than outside the realm of what is common in a household. A shut door or even a 12" header could have slowed the smoke down, and then another 10-20 before you get to the ionization smoke at the foot of the stairs. . Watch it start to swirl around 30 seconds. It happens.
  19. Gary_602z

    Gary_602z Minister of Fire

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    I think I will try sleeping with a fire fighter!
    037-121564-S.jpg

    Gary:)
    firefighterjake likes this.
  20. bluedogz

    bluedogz Minister of Fire

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    Best of luck, Gary. :rolleyes:
  21. stee6043

    stee6043 Minister of Fire

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    This thread actually got me thinking about residential sprinklers too. Soooo many projects, so small a budget. I think I'll do a new batch of detectors next year but I do have sprinklers in my 5 year plan now. I have easy access to my attic where all the bedrooms are and it looks to be a pretty low cost (parts wise) system. I may even throw a head or two in my boiler room this winter as a test run.
  22. firefighterjake

    firefighterjake Minister of Fire

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    Our Fire Inspector did a half-sprinkler system install in his home . . . by this I mean it isn't an actual approved system, but he did plumb several sprinkler heads off the domestic water in the basement above his boiler. A good friend and co-worker meanwhile put a whole certified system into his home as he felt strongly about fire protection . . . of course he also has an in-law apartment that he rents out so that buys him some peace of mind as well knowing the attached apartment is protected.
  23. firefighterjake

    firefighterjake Minister of Fire

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    Not to go off topic too much in terms of Christmas tree fires, but . . .

    While Christmas trees can catch on fire and pose a significant risk (1 in 9 fires involving a Christmas tree results in a fatality which is a higher ratio compared to other fires) . . . it is worth noting that in an average year only 200 or so fires involve Christmas tree fires each year . . . despite the fact that over 30 million trees are sold each holiday season.

    Properly maintaining a tree is the key . . . cutting a couple of inches off the butt, keeping the tree well watered and keeping any combustion sources from the tree (since Christmas trees in themselves do not tend to spontaneously burst into flames.)

    In regards the above video . . .

    http://fire.nist.gov/tree_fire.htm

    http://fire.nist.gov/bfrlpubs/fire00/PDF/f00147.pdf

    As you can see there was a bit of a difference between the tree that was properly cared for . . . and the trees that were not watered for three weeks.
  24. btuser

    btuser Minister of Fire

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    Three weeks? My mother didn't take down the Christmas tree until the Easter Bunny came!
  25. Lewiston

    Lewiston Burning Hunk

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    When we built the house we planned on installing a sprinkler system until we found out the cost and number of pressurized tanks needed. Opted for a fire extinguisher at every exit. More effective than having a house full of these:

    IMG_6449.jpg


    Just one of the very few disadvantages of living in the boonies.

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