Smoke Height

[Jonas]

Hi Everyone

is there a way besides "Laye zoning device" to calculate smoke height?

let's say I have a rectangular building with a height of 10 meters (with a small louver in the bottom to avoid creating a pressure zone). I installed a layer zoning device in the middle from floor to ceiling. After enough time I can visually see the whole room is completely filled with smoke but the layer zoning device report 1.9 meters as smoke height (although I can see the smoke has reached to the floor). 

Is this because the "Laye zoning device" separates the hot layer from the bottom more cold one and reports that separation point as the height?

Thank you

[dr_jfloyd]

The idea that a fire makes two completely separate layers with uniform temperatures at the same height across a compartment is a simplifying assumption used in zone models. The reality is each layer has a range of temperatues and that layer height will vary over the floor of the compartment. The layer equation works from the assumption that there is a strong straitification and tries to define that separation point. If you don't have clear stratification, the layer device will still give an output. If you have clear stratification, but put the layer device in a bad location (in the fire plume for example), you can get an output that doesn't reflect the compartment as a whole. The rericulaiton flow due to the fire, numerical diffusion, flow from vent opentings, etc. can cause smoke to mix into the lower layer. You could supplement the layer device with a visual assessment using slice files of temperature and visibility in a plane that includes the layer device.  

[Jonas]

Thank you so much for your insight and detailed explanation

Besides visual inspection using slices, do you think having a  series of smoke detectors be a good idea? For example, installing one every 0.5 meters from the ceiling to the floor and checking the reported smoke percentage.

[dr_jfloyd]

Sure you could put a vertical rake of device to measure temperature and/or smoke and from that look to see if there are two layers and find the inflection point in the vertical profile of values.