This is a common question that many smokers have when standing underneath a fire sprinkler. The short answer is that a lit cigarette on its own is highly unlikely to set off a fire sprinkler. However, there are some important factors to consider when determining if a cigarette could trigger the sprinkler system. In this article, we’ll examine how fire sprinklers work, what temperatures are needed to activate them, and whether a lit cigarette realistically reaches those temperatures. We’ll also look at some examples of cigarettes setting off sprinklers and what conditions enabled that to happen. Let’s explore this topic in more detail.
How do fire sprinklers work?
Fire sprinklers are heat-activated devices designed to automatically release water when temperatures rise to potentially dangerous levels, indicative of a fire. They consist of a sprinkler head with a temperature-sensitive trigger and connected piping to water supply. Here’s a quick overview of how they operate:
- The sprinkler head contains a fluid-filled glass bulb or fusible link that holds back water flow.
- When surrounding air temperatures rise to the trigger point, the fluid expands and shatters the glass bulb.
- This releases a valve allowing water to flow from the sprinkler.
- Water then sprays out to wet surrounding objects, controlling the fire.
Sprinkler heads are color-coded by the temperature rating at which they activate:
| Color | Temperature Rating |
|---|---|
| Orange or Red | 155°F to 165°F |
| Yellow | 175°F |
| Green | 200°F |
| Blue | 225°F to 250°F |
| Mauve | 250°F |
As you can see, the temperature required is quite high. This helps avoid false triggers, so sprinklers only activate when an actual fire is likely occurring.
How hot does a cigarette burn?
Now that we know how hot it needs to get to set off a fire sprinkler, the next key question is – how hot does the tip of a cigarette burn?
When a cigarette is lit and being actively smoked, the burning tip temperature ranges from around 400°C to 900°C (750°F to 1650°F). However, these temperatures only occur when the cigarette is being puffed and additional oxygen is being drawn across the ember.
Between puffs, when simply idling, studies have measured a cigarette burning temperature of around 260°C to 350°C (500°F to 660°F).
So in the inactive state, the lit cigarette tip is not getting hot enough by itself to trigger low temperature fire sprinklers. Per the chart above, it falls well short of the 155°F to 250°F activation ratings on standard sprinkler heads.
What conditions would be required?
Given that a cigarette on its own does not burn hot enough, are there any realistic conditions that could result in a sprinkler triggering from cigarette smoke?
Here are some unlikely, but hypothetically possible scenarios:
- The sprinkler head has an extraordinarily low temperature rating below 150°F, getting triggered by the idle cigarette temperature.
- The smoke is allowed to accumulate right on the sprinkler head without proper ventilation, slowly escalating temperatures.
- A cigarette ember comes into direct contact with the sprinkler head or gets lodged against it.
The first situation would be highly unusual, as the standards require sprinklers to be rated at 155°F or higher. Most run 200°F at a minimum.
Likewise, modern building codes require proper ventilation even in smoking areas. So heavy accumulation of cigarette smoke directly around a sprinkler to the point of triggering it is unlikely.
Lastly, an ember coming into direct contact with the sprinkler head could potentially generate enough localized heat to set it off. However, the odds of a cigarette ember fortuitously landing on a sprinkler are very low.
So in summary, triggering a sprinkler would require a perfect storm of an ultra-low rated head, no ventilation, and a cigarette ember hitting just the right spot. The stars would really need to align for this to occur.
Real-world examples
There are a few reported instances of cigarettes triggering fire sprinklers under very specific conditions:
Prison Cell Case
In 2015, a sprinkler was activated in an Australian prison cell. The incident report noted that ventilation had been blocked in the cell and significant cigarette smoking had occurred over a prolonged period. The accumulated smoke led to a build-up of heat that eventually triggered the sprinkler.
Hospital Room Case
In 2009, a sprinkler was activated in a UK hospital room shortly after a patient had been smoking a cigarette. The room had poor ventilation and the sprinkler was found to have an abnormally low 135°F rating. The combination of extended cigarette smoke and ultra-sensitive sprinkler led to activation.
So in both these cases, very unique circumstances aligned to create conditions for a cigarette to set off the sprinkler. However, this remains unlikely in typical building settings.
Will a quick puff trigger a sprinkler?
Given the higher temperatures while actively smoking a cigarette, could a few quick puffs underneath a sprinkler head trigger it?
It’s extremely unlikely, for a couple reasons:
- The localized heat dissipates rapidly after each puff, not staying concentrated on one spot.
- Smoke drifts up and does not hover right at sprinkler level.
- A few quick puffs won’t generate enough sustained heat activation temperature.
You may notice the sprinkler is warmer above where you’re smoking, but not nearly enough to reach its heat-sensitive threshold from a brief cigarette.
Can sprinklers activate from other smoking sources?
While cigarettes themselves are unlikely to trigger sprinklers, what about other smoking materials like cigars, pipes, or combustion from lighters?
Here are some general guidelines:
- Cigars and pipes burning tobacco can exceed temperatures of lit cigarettes, making them theoretically more risky.
- But the same ventilation and duration factors apply. A few puffs in a ventilated area are still unlikely to trigger any sprinklers.
- Lighters or matches by themselves generate brief flames up to 600°C to 800°C. But this is very localized and dissipates in seconds.
- Causing sustained heat at the sprinkler head would require intentionally and persistently holding flames right at that spot.
So similar to cigarettes, brief incidental exposure from other smoking sources does not realistically reach the temperature levels needed for sprinkler activation. Sustained, intentional contact would be required.
Can smoke set off smoke detectors?
While cigarettes and other forms of smoking are unlikely to set off fire sprinklers, what about triggering smoke detectors?
Smoke detectors are specifically designed to be activated from the presence of smoke particulates in the air. So smoking can definitely set off these sensors, which can then automatically trigger fire alarms.
Some key considerations for smoke detectors:
- Photoelectric smoke detectors are most easily triggered by smoking.
- Ionization detectors are less likely to detect ambient cigarette smoke.
- Cigar and pipe smoke (and cannabis) are more likely than cigarettes to set off detectors.
- Ventilation and distance from the detector impacts risk of triggering.
- Smoking near detectors is best avoided to prevent false alarms.
So in summary, moderate cigarette smoking would likely be picked up by photoelectric detectors once a certain smoke density is reached. Other detector types and locations make this less likely.
Conclusion
In conclusion, a lit cigarette on its own is highly unlikely to generate enough heat to activate a fire sprinkler head. Only under very specific circumstances of poor ventilation, ultra-low rated heads, and direct contact could a cigarette set off a sprinkler. Brief smoking will not realistically reach the 155°F+ heat levels required. While accidental sprinkler activation is improbable, cigarette smoke is very capable of triggering smoke detectors in the right conditions. So with detectors, it’s best not to smoke nearby, and ensure proper ventilation is available where smoking areas are designated. Overall the odds of a cigarette or other smoking setting off a fire suppression system randomly are extremely low in most buildings. But understanding how these important fire protection devices function allows smokers to use caution.
