calculate a distance between radiant -sensing fire detector and the fire release

[zarroukbouhlel]

hi everyone , could you help me , how i calculate a distance between radiant -sensing fire detector and the fire release according to the NFPA72 , appendex B . thanks

[DM2]

Something is missing from your question but i’m not sure what it is as I’m not sure what your trying to accomplish. From a risk based approach, you would first want to determine the tolerable heat flux the “object” can withstand (see the below publication link)

[link Point to another website Only the registered members can access]
With regard to determining flame detector sensitivity, have a look through the “New Jersey” chapter of SFPE, publication “Fusible Link”. In 2004 John Cholin published five (5) articles (spanning between 2004 and 2005), that walk you through the process. These articles appeared in the above referenced “Fusible Link” news letter, under the title “The Case for Performance Metrics for Fire Protection Devices”, and covered the requirements of NFPA 72, Annex B.5

• [link Point to another website Only the registered members can access]

• [link Point to another website Only the registered members can access]

• [link Point to another website Only the registered members can access]

• [link Point to another website Only the registered members can access]

• [link Point to another website Only the registered members can access]

There are a number of publications that address the the maximum amount of "heat flux" that something and tolerate, and there's far more to laying out flame detectors than one typically considered, but that's a longer discussion.

[zarroukbouhlel]

hi DM2 , thank you for your response , my problem is how can i solve this equation k c At exp(-ζdt)/dt2 = k c Ad exp(-ζ dd)/dd2 , in order that i determinate
''dt=the distance at which the detector can detect the design fire''
my questions :
how can i determinate the values of Ad and dd ?
what deas it means ''listing fire test '' ?
could you share a link that explain this issues ?

thank you in advance.

[DM2]

The "Listed" fire test, is the test performed by the testing agency, such as FM. You obtain this information from the flame detector manufacture, and it should be published in the manual for the specific flame detector. Your looking for something along the lines of "1ft x 1ft" nHeptane pan fire, at 200 ft, in X seconds. If you're using a detector that was tested to EN54, and not the FM standard, you may not find this information. The "pass/fail" criteria for either the EN or FM test, is 30 seconds, however for manufactures testing to FM, they'll typically state "15 seconds", or something similar. I've seen one manufacture state 200' in 5 seconds, and 270' in 15 seconds for the same detector with the same sensitivity settings.

The manufacturers don't publish the value for ζ (extinction factor), in fact some very reputable flame detector manufactures don't even know what this is. This value, however, is intended to represent the atmospheric conditions at the time of the test. Imagine if you tested a flame detector in the summer with high humidity (98%) and then did the same test, with the same manufacture, when the humidity was low (30%). Theoretically, the moisture in the air will affect the amount of radiated energy incident on the flame detector (there are actually several papers written on the subject). Next, have a read of the paragraph following equation 3, from the 1st link.

The term "A", is typically used to note the area of the flame. If your pan fire is 1 x 1, and the test fuel is nHeptane, than the height of the flame is about 4' 3" (It's been a while since I did the math, but the formula for flame height can be found in the SFPE handbook). With this, you need to calculate the area of the flame to get the value for "A". For more information on this, see the "Fusible Link", January 2005 edition (should be the 3rd link in my post). The 2nd page of this link, notes the "t" (subscript) is the area of the test fire, and "d" is the area of the design fire.

The purpose of posting the first link is that from a risk approach, you need to first determine the tolerance of your hazard in terms of heat flux output of the flame (how big is too big for the flame). This is your "d" value or "Design Fire Size". If you have a pressure vessel that is "uninsulated" and without a "water spray" system, you may determine that 750 kw is the maximum heat flux you can tolerate for 15 seconds before the tank begins to experience a BLEVE. You now need to work backwards to make sure that the flame can be seen by the flame detector (based on it's sensitivity setting, or "t" value determined by the FM test) and the distance the detector is from the potential flame. If the detector is 40' away, and there are obstructions between the detector and the design fire, the fire will eventually get to the 750 kw size, which would be large enough for the flame detector to see it (depending on the sensitivity setting).

Herein lies the rub...Flame detectors incorporate a number of different algorithms, one of which is flame flicker. The flicker typically occurs from 50% of the flame height upwards. If this upper portion of the flame is blocked from the view of the detector, the base of the flame could be larger than needed (At) to see the fire, however it will never respond because it's can't see the "flicker" and will assume it's black body radiation.

[zarroukbouhlel]

thanks for your explanation , my problem is near from the solution , it remain how can i determinate the fire release HRR , i don't know i use the max of HRR from the rate heat release curve or what ? , also i searched in some flame detectors datasheet but i dont found the test fire relitives values provided by the testing agency .
thanks in advance

[zarroukbouhlel]

thanks for your explanation , my problem is near from the solution , it remain how can i determinate the fire release HRR , i don't know i use the max of HRR from the rate heat release curve or what ? , also i searched in some flame detectors datasheet but i dont found the test fire relitives values provided by the testing agency .
thanks in advance

[DM2]

Pickup a copy of the SFPE Handbook as it has all of the formulas. Then do a "Google" search for the term "Heat Release Rate Formula" and you come across a number of references, including the below PDF's:

• [link Point to another website Only the registered members can access]

• [link Point to another website Only the registered members can access]

• [link Point to another website Only the registered members can access]

...the below web sites:

• [link Point to another website Only the registered members can access]

• [link Point to another website Only the registered members can access]

• [link Point to another website Only the registered members can access]

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  [link Point to another website Only the registered members can access]

...the below spreadsheets from the last of the NRC link above:

• Chapter 4. Estimating Wall Fire Flame Height

  [link Point to another website Only the registered members can access]

  [link Point to another website Only the registered members can access]

• Chapter 5.1 Estimating Radiant Heat Flux from Fire to a Target Fuel at Ground Level under Wind-Free Condition Point Source Radiation Model

  [link Point to another website Only the registered members can access]

  [link Point to another website Only the registered members can access]

• Chapter 5.2 Estimating Radiant Heat Flux from Fire to a Target Fuel at Ground Level in Presence of Wind (Tilted Flame) Solid Flame Radiation Model

  [link Point to another website Only the registered members can access]

  [link Point to another website Only the registered members can access]

...and lastly the below YouTube Tutorials:

• [link Point to another website Only the registered members can access]

[zarroukbouhlel]

does anyone have the NFPA Fire Protection handbook?