# Fog Juice and Fire Alarms!



## JD (Mar 11, 2008)

In the 70's and 80's I used both dry ice and chemo-fog and fogged the heck out of some of the places we did and never had any problems with smoke detectors tripping. It's been awhile. Anyhow, I have an upcoming charity gig at a fire house, and when I mentioned we would be using fog, the fire chief told me that they answer a lot of alarms tripped off by detectors reacting to the use of fog machines. I found that surprising. It has been awhile so I though I would throw the subject up here. Has the nature of detectors changed in a way that may cause them to trip on fog? (or is this fire chief a little foggy himself?)


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## erosing (Mar 11, 2008)

I've never actually used fog in a vicinity that had a smoke detector...except for one, but it never set off the fire alarms. Though I have heard of it happening from a few friends.


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## SerraAva (Mar 11, 2008)

Depends on the type of alarms. A lot of new alarms are laser based, meaning that when a certain amount of smoke blocks the laser, the alarm goes off. Fog has real problems with these. Dry ice can also set off carbon monoxide and dioxide detectors. Most modern spaces built with the intent to have shows use heat sensors. The heat gets to a certain point and alarm goes off.

My advise would be advise the local fire marshal that you are testing fog/haze effects in a building to see if it will set off the alarm system. Then you try it out and see what happens. That, or you can try and get the specs of the building and see just what type/s of alarms they have in the building.


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## zac850 (Mar 11, 2008)

Heat fire alarms are wonderful because a fog machine will not set them off. I had a DF-50 (hazer) 2' away from a heat alarm, no problem.

The problem was the smoke alarm in the basement that tripped the alarm and called the fire department. Yes, smoke alarms can and will get tripped by haze or fog. Most theaters will disable the fire alarm in the theater during a show that needs haze or smoke for this reason.


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## len (Mar 11, 2008)

Yes, it's true. There's a whole variety of fire alarms that don't measure heat. They measure particulate in the air, they use laser beams, infrared, etc. Some towns won't allow haze/fog at all, others you have to pay the fire dept. to send someone over to stand there for the event.


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## PadawanGeek (Mar 11, 2008)

I have been to one concert where the smoke alarm went off because of the fog (laser detector), and one time one of my friends set off a smoke alarm with too much fog (i don't know what type of detector it was)


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## ndiaz (Mar 11, 2008)

yes, I'll add to this, we set off our school's fire alarm, because the fog was in the orchestra pit, coming through the pit holes. However, the ventalation system was on, and it was so strong, the smoke wasn't able to get out of the pit and then it set it off.


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## BillESC (Mar 11, 2008)

Shouldn't be much of a problem having the fire department disable their fire detection system and supply a Fire Watch.

In most newer commercial construction the smoke detectors are located in the HVAC system.


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## tgates (Mar 11, 2008)

JD said:


> In the 70's and 80's I used both dry ice and chemo-fog and fogged the heck out of some of the places we did and never had any problems with smoke detectors tripping. It's been awhile. Anyhow, I have an upcoming charity gig at a fire house, and when I mentioned we would be using fog, the fire chief told me that they answer a lot of alarms tripped off by detectors reacting to the use of fog machines. I found that surprising. It has been awhile so I though I would throw the subject up here. Has the nature of detectors changed in a way that may cause them to trip on fog? (or is this fire chief a little foggy himself?)



This is absolutly a problem and have been at a show where this was not taken care of when the client said it had, you can imagine the effect this had on the show. Any particulate matter can set them off, even just dust. Usually, you can get a fire watch at most venues for a couple hundred dollars, depending on how their system is set up.. and their willingness to help their costumers. They literally just have a firemen stand around and watch.

On the other hand, when we do shows with dry ice, we tend to just leave the smoke detectors on. Even though it could set off the new generations of smoke detectors, the nature of the fog seems to be that it dissipates before it's ever warm enough to rise up to where it could set any detectors off.


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## gafftaper (Mar 12, 2008)

My new theater has heat detectors in the theater itself which was great news. However, I discovered there are smoke detectors in the exhaust ducts. I'm told that it may be possible to disable them without going on fire watch as they are a backup to the heat detectors. Still haven't discussed that with the Fire Marshal.


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## TimMiller (Mar 12, 2008)

I have set quite a few fire alarms off with fog and haze. You have to watch out for oil based haze because it sets off carbonmonoxide alarms. I have set off laser alarms with a ladder before. They had them setup with beams shooting around the room and i setup a ladder to replace some lamps and beep alarms go off. The dumbest alarms made in my opinion. Heat alarms are the way to go in performance venues.


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## LD4Life (Mar 12, 2008)

I just recently did a show where, for the first time in my time doing lighting, I had to have the alarms turned off for the show. Luckily, the building TD knew about it and warned me when I mentioned haze. Its an IR system that is an absolute bear. I did find, however, that I could avoid setting it off when they were turned on by opening the doors between the scene shop and backstage and opening the door from the scene shop to outside to create a wind tunnel that cleared to excess haze. Just a little tip if anyone ever needs it, create a wind tunnel to clear the excess.


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## JD (Mar 12, 2008)

Kind of suspected that. The older detectors in use back then used a little chunk of radioactive material and looked for ionizing particles, so they would not trip on fog. Since I have not seen the "Caution- Contains Radioactive Material" sticker on newer units, I figured they redesigned them. Makes sense that a laser would not know the difference between smoke and fog. I guess the old Fire Chief wasn't just blowing smoke!


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## kwotipka (Mar 12, 2008)

Fog, Haze, a tech sneaking off to smoke in the wrong place. All these things will cause headaches with a production unless all parties involved know what and when it will be used. Most commercial venues have provisions to disable the sensors in the area but will require a "Fire Watch". It usually does cost for the fire department to provide this service but it is nothing compared to the fines in some places for using a fog/haze effect without permission / permit.

This is definitely not one of those "do now ask permission later" kind of things.

kw


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## Van (Mar 12, 2008)

Adding to what other have said, Better safe than sorry. One building I used to work in was an automatic 5 alarmer, if you set that off accidentally, you heard about it. from the book keeper! < Very expensive fine for false alarming.> 
One place I worked in had a laser based system that shot a beam around the room one foot below the lowest point of the ceiling. Great, until one of the riggers broke a beam trying to tie into a rig point built into the ceiling... Do contractors ever communicate with each other ? 

If at all possible , and check with the local authorities for regulations, disable the smoke sensors, post a fire watch, then re-able the system as soon as the roo is clear. 

Just a little factoid, smoke alarm manufacture-ers used to be the the largest consumers of Americinium, the radioactive isotope used in smoke dectectors.


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## LD4Life (Mar 12, 2008)

It was really interesting with that last show I was talking about. The local fire marshal actually didn't require us to have a fire watch, so we didn't have to pay a penny. We just got his permission to turn off the system for certain blocks of time.


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