Stratification and smoke detectors

[DavidCR]

I have a small storage house. Where I want to know if the stratification effect is an issue that should be considered to locate smoke detectors.

Area: 15m x 18m. Peaked roof. Highest peak ceiling height 7m, lowest ceiling height 4.7m (slope 17deg). The ceiling gets hot due to sun over the metallic roof, no suspended ceiling, no air conditioning, just the metallic roof.

Considering the height of this roof 4.7 to 7m that is not too high. I´m looking for criteria on if stratification should be or not considered in this case to place additional detectors?

I´ve seen places where they have placed smoke detectors 1m bellow the roof assuming stratification conditions will be met but without any analysis.

NFPA 72, annex B include some info, but I appreciate if somebody has a more practical approach or rules of thumb.

 

[stookeyfpe]

It's not a big building, and stratification normally comes into consideration when one is dealing with stack effect in high-rise buildings or large atria. You have neither condition.

I would recommend using the prescriptive requirements because I'm not seeing anything that indicates stratification is a problem. If I'm missing something let me know.

 

[pipesnpumps]

What is the design fire? The height the smoke rises depends on the temp of the smoke as it rises. Smoke entrains room air as it rises. The strength of the fire plume depends on the heat release rate..

A smoldering fire for example could possibly stratify in your warehouse since the smoke will cool. But maybe you aren't concerned about that small of a fire..

I agree with stookey that it is not normally an issue except in tall buildings (where plume has more distance to cool) but if you want optimal detection for all scenarios it is not a simple answer...

Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.

 

[DavidCR]

Yes, the expected items to store might not be a big load.

Machinery replacement parts in small carton boxes/plastic bags, no big quantities.