Will a fog machine set off a fire alarm?

Fog machines are a great way to enhance any event by adding a nice touch to your lights. They come in many types and sizes. Thus knowing if a fog or smoke machine will set off a fire alarm or smoke detector is often difficult.

As a general rule, a fog machine will trigger fire alarms as most systems detect particles and not heat. Fogs, smokes, and haze will set off the alarm of such smoke detectors. The only way not to set off the alarm is to use a low-lying fog machine or change the detectors into heat sensors.

Fog machines and the various sort of fire alarms

To make things clear, let’s start by describing the different types of fog machines:

Low fog machines:
These machines create a low-lying fog to create a “walk on clouds” effect. They are very popular for Halloween and wedding opening dances. It creates a very thick smoke that stays on lower grounds. These machines have a cooler based on either dry ice or liquid CO₂.
Fog or smoke machine:
These create a thick smoke that fills the entire room even at heights. They are the most common ones, the ones you see at parties or clubs. They are the less expensive machines. Please note the two terms are used interchangeably.
Hazer:
As the name implies, create a haze around the entire room. Much less thick than fog machines they are oil-based or water-based. As being much less opaque, you won’t see it directly but will definitely notice its effects on lights and lasers.

All these machines produce either a cool or tempered output. They are not “hot” excepting at the nozzle area. What differentiates these machines regarding alarms is the thickness of the effect and its capacity to spread.

Then you have 4 types of sensors involved in fire alarms:

Ionization smoke detectors:
They have a constant electrical current running between two plates that is interrupted if smokes come in. It will be triggered if enough particulates enter the apparatus.
Photoelectric detectors:
Very similar to ionization detectors. The particulates will stop a beam of light in the apparatus. The alarm is set off when the receiver no longer receives the light.
Heat detectors:
As the name implies set offs when the temperature increases too much. They are not triggered by particulates.
CO detectors:
Detects carbon monoxide that fires may also produce. They are not triggered by random particulates.

Then you can have any combination of the various systems above with different triggering rules.

As you have noticed, the main difference between sensors is the ability to be triggered by particulates. Fog and haze are particles by nature and will therefore set off ionization and photoelectric detectors. However, haze machines have smaller particles, they will set off alarms less easily. On the other hand, low fog machines won’t let the particulates go in the detectors since most of them are placed at heights. They are very less likely to set off alarms.

The most common sensors are unfortunately the ionization and photoelectric sensors. They are indeed the more effective even though they will produce false alarms with fog machines.

Here is a table summarizing which smoke machines will set off alarms:

	Low fog machines	Fog and smoke machines	Haze machines
Ionization smoke detectors	Not likely	Very likely	Likely
Photoelectric smoke detectors	Not likely	Very likely	Likely
Heat detectors	No	No	No
CO detectors	No	No	No

How to make sure the fog machine will not set off the alarm

Fire alarms made of carbon or heat sensors should usually have no problem with fog machines. However, knowing the type of detector used is not always easy. Moreover, some systems combine different kinds of sensors together and can be configured differently (different trigger levels, etc). In short, every situation is different and a system that gives no issue at one location may be a disaster somewhere else.

Therefore, it is always better to test your fog machine before any gig. Ask the organizer of the event where the smoke detectors are and place the machine as far away from them. Ask or search where the switch of the alarm is in case you set it off. Indeed, a fire alarm can make a direct call to the nearby fire department who may come if the alarm runs long enough. Unfortunately, they can charge you if they come for a false emergency.

So be prepared to turn off the alarm quickly during your tests. I am not saying to turn off the detectors but to be prepared to turn them off just in case. You may even invite a fire marshal with you so that he can tell the fire department to ignore the alerts during the testing.

To reduce the risk of setting off an alarm, you can also build a cooler around the nozzle. Indeed cooled fog will stay at lower heights and thus reduce the risk of running into sensors.

Some places with recent detection systems can have a combination of sensors that can be switched on or off. For instance, they can be set up for particles and heat together most of the year but can be set up for heat only during events. For this reason, it is always a good habit to ask the owner of the venue about the fire detection system. Make sure to never touch the alarm system yourself and always with the owner’s consent.

Will a haze machine trigger a fire alarm?

Though haze machines make a less dense fog, they can trigger fire alarms. It is less likely than a regular fog machine thanks to its smaller particles. Things may vary depending on the room, the sensors, and the amount of haze. Oil-based hazers are less likely to set off alarms than water-based ones. Here is a great one on Amazon.

Haze machines will not trigger fire alarms based on heat or carbon detectors. But knowing the type of sensors is not always easy so I still recommend making small tests before a gig.

Can a fog machine set off sprinklers?

A fog machine will not set off sprinklers used alone. Indeed sprinklers can be triggered either manually or by heat. However, it is not uncommon to have sprinklers coupled with other systems in a fire alarm. Therefore, if the fire alarm does have smoke detectors, it can then set off the sprinklers.

Every fire alarm system is different and thus it is always best to ask the venue and to always perform tests beforehand. The same thing applies for hazers, they would not set off sprinklers used alone but can in a more elaborate system.

Can I turn off the fire alarm then?

It is not recommended to turn off a fire alarm but it may be done. The procedure is to contact a nearby fire marshal. The latter may accept under the condition that the area where the sensors are deactivated to be closely monitored. Most will require to be monitored by a fire marshal itself.

It is not guaranteed the fire marshal accepts but that’s worth asking. It may cost you extra but this is worth it in my opinion. Of course, the procedure may vary according to venues. For instance, if you can’t turn off the alarm by room but only globally, there is a good chance to be refused. A fire in a kitchen is much more likely and can spread easily for instance. If you can turn off the sensors where the party goes only, it is way easier to handle and may be accepted.

In fact, according to NFPA regulations, what is required is a way to notify the fire department in the event of a fire. It can either be a smoke detector or a human. Smoke detectors are widely used because they run endlessly and are more reliable for assurances.