Ask a Question forum: Mirror and fire safety

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Montpelier, VT
ABoyles
Jun 19, 2017 6:42 AM CST
Do I need to worry about fire safety when placing a mirror in my yard? Seems like it wouldn't be an issue unless the mirror was magnifying the light which a flat mirror wouldn't do...Thanks for any insight!
Name: Philip Becker
Fresno California (Zone 8a)
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Philipwonel
Jun 19, 2017 8:13 AM CST
It could start a fire under right conditions.
Anything i say, could be misrepresented, or wrong.
Name: Porkpal
Richmond, TX
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porkpal
Jun 19, 2017 9:16 AM CST
I wouldn't worry.
Porkpal
Name: Karen
NM (Zone 7b)
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plantmanager
Jun 19, 2017 9:34 AM CST
I've always put mirrors in my gardens and had no problems.
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Name: greene
Savannah, GA (Sunset 28) (Zone 8b)
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greene
Jun 19, 2017 11:49 AM CST
Just want to say that, yes, a mirror given the right conditions, can cause a fire.
Normally, I would think of a magnifying glass increasing the rays of the sun, concentrating them to a point to start a fire (think of evil children burning ants by using the sun and a magnifying glass, yuck!) but yes, a mirror combined with intense sunlight can start a fire.
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Name: tarev
San Joaquin County, CA (Zone 9b)
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tarev
Jun 19, 2017 12:26 PM CST
I agree it may cause fire. Unless it is not focusing on the sunlight directly then it's okay. Even mirrors indoors can cause fire if that intense light gets projected on curtains and other flammable items.
Name: Porkpal
Richmond, TX
Charter ATP Member I was one of the first 300 contributors to the plant database! Keeper of Poultry Farmer Roses Raises cows
Garden Ideas: Level 2 Celebrating Gardening: 2015 Plant Identifier
porkpal
Jun 19, 2017 12:45 PM CST
We need some science here. I don't see how reflected sun would be hotter than direct sun.
Porkpal
Name: tarev
San Joaquin County, CA (Zone 9b)
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tarev
Jun 19, 2017 12:45 PM CST
just browse on the net, lots of info there if you want further info
Name: Sandy B.
Ford River, Michigan UP (Zone 4b)
(Zone 4b-maybe 5a)
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Weedwhacker
Jun 19, 2017 9:21 PM CST
Tarev, do you have any particular sites in mind? I looked at a few and it really seems pretty unlikely to start a fire, or at least equivocal.

Like Porkpal, my mind says that light reflected from a mirror would lose energy and be highly unlikely to cause a fire... but it wouldn't be the first time if I was wrong. (Light passing through a magnifying lens of some sort, of course, would be a different situation)
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Name: Karen
NM (Zone 7b)
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plantmanager
Jun 19, 2017 9:30 PM CST
I've used mirrors outside in Arizona sun for years. No fires, but they do get ruined by loss of silvering. I love them on walls, reflecting the garden, and hanging in mobiles. I know about fire and magnifying glasses, but have never had a problem outdoors with mirrors. If it was such a problem, you'd think mirrors on cars would be starting fires.
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Name: tarev
San Joaquin County, CA (Zone 9b)
Always count your blessings in life
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tarev
Jun 19, 2017 9:45 PM CST
Sandy, some sites about mirror and fire:

http://www.cheshirefire.gov.uk...

https://www.successfulgardende...

http://www.ehow.com/how_485710...

http://www.getwestlondon.co.uk...

a youtube video : https://youtu.be/D2ym8wt5NWo
Name: Sandy B.
Ford River, Michigan UP (Zone 4b)
(Zone 4b-maybe 5a)
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Weedwhacker
Jun 19, 2017 10:02 PM CST
Thanks, Tarev.

The 2 UK sites refer to a magnifying vanity mirror (a makeup mirror).

The YouTube site refers to a magnifying glass.

The SuccessfulGardener site doesn't make much of a case for mirrors being responsible for starting fires, but does bring up an interesting point about possible injury to birds.

The EHow article states "A mirror is not the easiest thing to make fire with, but in a pinch, it will create the right conditions for fire" (and I'm not really sure how much credibility to give that article.)

I continue to think that the likelihood of a mirror in the garden starting a fire is extremely low. However, the issue of birds running into the mirrors is certainly a consideration!
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Name: tarev
San Joaquin County, CA (Zone 9b)
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tarev
Jun 20, 2017 12:30 AM CST
Sandy, you asked for links, so I gave you some. It is up to you to research some more if you want. The general gist of all of them, glass objects, which includes mirrors may help cause fire.
Name: Baja
Baja California (Zone 11b)
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Baja_Costero
Jun 20, 2017 10:30 AM CST
There were a couple of MythBusters episodes dedicated to this subject, where they were trying to use mirrors to cause fire on purpose, and it was actually ridiculously hard to get the target ablaze, even when primed for action. It required many (many) mirrors and a focusing mechanism whereby they were all aimed at the same target. Admittedly they were going for an effect at distance, but I think the principle still holds true in the range of a few feet. Reflected sunlight is only going to be weaker than direct sunlight, unless it is focused or amplified. That is the principle behind solar power arrays which use mirrors.

The sum total of direct sun and reflected sun (in the case where it might be reflected into a sunny area) would be less than 2x direct sun. That is roughly the difference between max sun intensity in winter vs. summer, here in the subtropics.

A regular flat mirror in the garden is not going to cause fire without some freak mechanism taking place, and something very flammable on the other side. Not to say it couldn't happen. Tarev, if you can provide any links which answer the question, please do so. It is one thing to say things "may cause fire" and another to get at the question of whether there is any actual danger.
[Last edited by Baja_Costero - Jun 20, 2017 12:30 PM (+)]
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Name: Sandy B.
Ford River, Michigan UP (Zone 4b)
(Zone 4b-maybe 5a)
Charter ATP Member I was one of the first 300 contributors to the plant database! Garden Sages Million Pollinator Garden Challenge Seed Starter Vegetable Grower
Greenhouse Region: United States of America Region: Michigan Enjoys or suffers cold winters Butterflies Birds
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Weedwhacker
Jun 20, 2017 10:39 AM CST
tarev said:Sandy, you asked for links, so I gave you some. It is up to you to research some more if you want. The general gist of all of them, glass objects, which includes mirrors may help cause fire.


I appreciated the links, Tarev -- I didn't mean to make it sound like I was holding you responsible for their content Smiling

Those were the same types of links that I had found before I asked what you had seen, I just thought maybe you had something more conclusive than I had come across.

Although I think the idea of having mirrors in the garden is cool, and I don't think they would be more likely to cause a fire than, say, hanging old CDs on a fence to scare the deer, the possibility of birds running into them and injuring or killing themselves would keep me from putting mirrors out; we have enough birds run into the windows around here (although a lot less since I removed a bird feeder that was near some sliding patio doors, several years ago).

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Name: Jean
Prairieville, LA (Zone 9a)
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Moonhowl
Jun 20, 2017 11:47 AM CST
Flat mirrors are not likely to cause fires as the sun's rays are spread out rather than concentrated. Parabolic or concave mirrors concentrate the sun's rays and are used by survivalists, campers and boy scouts to start fires.

The sun's rays must be concentrated in one small area to achieve the energy necessary to produce a flame.

https://en.wikipedia.org/wiki/...

a mirror reflects, a lens refracts. A magnifying lens can be used to start a fire, your decorative garden mirror poses a greater threat to birds than fire starting.
Name: greene
Savannah, GA (Sunset 28) (Zone 8b)
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greene
Jun 20, 2017 1:10 PM CST
ABoyles said:Do I need to worry about fire safety when placing a mirror in my yard? Seems like it wouldn't be an issue unless the mirror was magnifying the light which a flat mirror wouldn't do...Thanks for any insight!


Not every mirror is completely flat; some have imperfections. Since the answers you have received on this thread are all over the place, perhaps you should contact your local fire marshall. After all, we here on NGA are merely gardeners, not experts on the causes of fires. Thumbs up

Sunset Zone 28, AHS Heat Zone 9, USDA zone 8b~"Leaf of Faith"
Name: Jean
Prairieville, LA (Zone 9a)
Charter ATP Member Plant Identifier The WITWIT Badge Garden Sages Celebrating Gardening: 2015
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Moonhowl
Jun 20, 2017 5:34 PM CST
You are correct in that @ABoyles should check with the local Fire Marshall. There may be local restrictions in effect that we could not know and ABoyles can be safely assured by calling the local fire Marshall. Thumbs up

I asked my husband, he is fire safety and fire and rope rescue and an emt at his plant. He is the one who confirmed my info on Concave, Convex, Flat and Parabolic mirrors.
Name: Philip Becker
Fresno California (Zone 8a)
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Philipwonel
Jun 21, 2017 3:32 PM CST
Hay there gang. I'm staying with my 1st response. For anybody, that bothered to, even read it.
So !!! I'm going to ask this !
What ? Are, you, going to tell, your homeowerers agent ??? Well !!! People at NGA ! Said ! It was unlikely, etc, etc. !!!
Insurance ! Is gonna, laugh, in your face.
Anything i say, could be misrepresented, or wrong.

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