# Presentation: 830614

## SMOKE DETECTOR PERFORMANCE FOR LEVEL CEILINGS WITH DEEP BEAMS AND DEEP BEAM POCKET CONFIGURATIONSDaniel J. O’Connor P.E.Schirmer Engineering Corporation 

## Acknowledgements

- Fire Protection Research Foundation (FPRF) & Supporting Patrons
- Fire Detection and Alarm Research Council
- FPRF Appointed Project Technical Panel
- NFPA 72 Initiating Devices Committee

- Vision Systems Ltd. (Aus.)
- Ming He, MIEA
- Yun Jiang, MIEA
- John Vythoulkas
- Tawfeeq Al-Farra

- Schirmer Engineering
- Ervin Cui, Ph.D., P.E
- Matthew J. Klaus
- Chen Su, P.E.

## Current NFPA 72 Spot Smoke Detector Rules for Solid Beams 

**≤ ****12 inches**

**≤ ****12 feet **

**Parallel direction -30 ft. guideline **
**Perpendicular** -**15 ft spacing **

## Why Most Questioned Requirement

**90 feet**

## Review of Previous Work

- NFPRF Sponsored NIST’s CFD work in 1993-94
*International Fire Detection Research Project, Field Modeling: Effects of Flat Beamed Ceilings on Detector and Sprinkler Response; Technical Report Year 1, October 1993*
- Significant in identifying flow effects resulting from parallel channels due to beams
- Scope was limited, CFD modeling was computational intensive in early 1990’s

## Scenarios of 1993 Work

- Majority of Scenarios
- 11 ft. ceiling
- Fire to ceiling distance, constant at 8 ft.
- Beam depths 0, 4, 8, 12, 24 inches
- Beam spacing varied
- Few high ceiling scenarios
- 28 ft. ceiling
- Beam depth constant at 12 inches

- 8 ft.

- 11 ft.

- 28 ft.

## Extract from 1993Technical Report Year 1

**Extract from 1993****Technical Report Year 1**

- Activation – 13 ̊ C rise only
- Criteria for detector activation narrowly defined using a threshold fire size
- Medium growth 100 kW fire
- Medium growth 1 MW fire
- No comparison to the expectation of smoke detectors spaced per 30 foot guideline
- No understanding of how field conditions would change if examined 5, 10, 30 or 60 seconds later
- No review of gas velocities at smoke detector
- Most scenarios with parallel channels, no consideration for constraining effects of corridor walls or beam pockets

## Objectives - Methodology

- Identify appropriate spot smoke detector activation thresholds
- Optical density
- Temperature rise
- Flow velocity
- Best Source for data on thresholds - Recent work by Geiman (Masters thesis) and Geiman & Gottuk (paper in Fire Safety Science)
- Identify baseline detector performance
- 30 ft x 30 ft spacing on unconfined flat ceiling
- Vary performance with increasing height
- Perform modeling & examine field conditions
- At postulated smoke detector locations
- Determine likelihood that field conditions would result in activation
- Compare postulated detectors with
- Baseline detector performance
- Spot detector activation thresholds
- Reduce the data to usable format – results, trends, conclusions

## Review of Work by Geiman and Geiman & Gottuk – Flaming Fires Only

|  | Predicted Alarms | Over & under Predictions | Alarms within + 60 seconds | Evaluation for Beam Study |
| --- | --- | --- | --- | --- |
| Nominal Sensitivity per UL 217/268
~ 1- 3%  Obs/ft
~.014 - .043  OD/m | High % predicted | 3:2 ratio over : under | 30-40 % | Not sufficiently conservative |
| Max. Black Smoke OD
10% Obs/ft
0.14 OD/m (closer to 0.15) | 30% | Almost all over-predictions
+1000 % -2000% error | <10% | Too conservative, unrealistic view of detector performance for flaming fires |
| 20th percentile Average OD Alarm Threshold
0.007 + OD/m  (ion)
0.031 + OD/m  (photo) | High % predicted | Majority under-predicted | 63% ion
49% photo | Under- prediction not suitable for code requirement study |
| 80th percentile Average OD Alarm Threshold
0.072 + OD/m  (ion)
0.106 + OD/m  (photo) | Fewer predictions than 20th percentile Average OD Alarm Threshold | More over-predictions than 20th percentile Average OD Alarm Threshold |  | Tendency for over prediction suitable for code requirement study, but not overly conservative as 0.14 OD/m |

## Review of Work by Geiman and Geiman & Gottuk – Flaming Fires Only

|  | Predicted Alarms | Over & under Predictions | Alarms within + 60 seconds | Evaluation for Beam Study |
| --- | --- | --- | --- | --- |
| 4 degrees C Temperature  Rise
 | 100 % predicted | 4:1 over/under –ion
1: 3 over/under –photo | 57% ion
30% photo | representative of a conservative threshold for ionization detection |
| 13 degrees C Temperature  Rise | 90% | Ion vast majority over-predictions
Photo 1:1 | Very few | representative of the typical photoelectric detector |
| Flow Velocity
0.15 m/s 
Mean 0.13 + 0.07 m/s (from GG data review) | 100% predicted | Slight over-predicted | ~ 40 % | Use mean value to review velocity field conditions to be assured of sufficient velocity at for smoke entry into detector |
| 80th percentile Average OD Alarm Threshold
0.072 + OD/m  (ion)
0.106 + OD/m  (photo) | Fewer predictions than 20th percentile Average OD Alarm Threshold | More over-predictions than 20th percentile Average OD Alarm Threshold |  | Tendency for over prediction suitable for code requirement study, but not overly conservative as 0.14 OD/m |

## Baseline – 30 ft. Guideline Spacing

**Elevation View**

**Plan View**

## Baseline – 30 ft. Guideline Spacing

## Baseline Ceiling Jet Development12 ft Ceiling Ht., Red ≥65 ̊ C , Green ~ 40 ̊ C 

## CFD Grid System

## Measurment Points

## Corridor Scenario 2

- In this scenario 12 inch deep beams interrupt the ceiling surface every 3 feet.  Temperature rise exceeds the threshold of 13oC and 4oC during an early time frame and all locations exceed that of the baseline detector.  Optical density exceeds that of the baseline for all detector locations.  Detector locations within pocket or on the bottom of the beam experience comparable optical density valu

## Time Shift – Δt Relative to Baseline

## Corridor Ceiling Jet Development12 ft Ceiling Ht., Width 5 ft., Beam Depth 12 in. -  Red ≥65 ̊ C , Green ~ 40 ̊ C

## Corridor Scenario 18

- : In this scenario 24 inch deep beams interrupt the ceiling surface every 3 feet.  Introducing a 24” beam at the 18 ft ceiling height shifts the baseline 15 to 20 seconds before the noted detector locations.  However, all detector locations relatively quickly exceed the temperature rise and optical density values observed for the baseline

## Trends Shown

**Trends Shown**

- For a 5 ft wide corridor, the optical density at all locations along corridor reaches into the blue range and exceeds the baseline in 30 seconds. The comparison graph for the 60 second time frame illustrates trends resulting as steady state conditions are reached.  At 60 seconds for any given ceiling height grouping the general trend is that optical density values tend to increase as beam depth increases.  This is attributable to a reservoir effect that allows soot concentration to build in the deep beam pockets.  As ceiling height groupings of data are reviewed left to right (from 9 ft to 18 ft) the trend is that optical density values are reducing in value due to the additional entrainment into the plume that results with increasing ceiling height.  In all cases shown it is evident that at 60 seconds all postulate detector locations would be expected to alarm and exceed value for the baseline case

## Trends Shown

- For a 12 ft wide corridor, the optical density at all locations along corridor reaches into the green range and exceeds the base line in most cases in 60 seconds. Some turbulence impacts are observed at early time frame (30 seconds).  Also Optical density value shows more entrainment and dilution results in this wider corridor scenarios as compared to the 5 ft wide corridor scenarios

## Reservoir Effect – Increases OD

- Top Graph
- Corridor Smooth Ceiling
- OD rise earlier than unconfined smooth ceiling baseline
- Bottom Graph
- 12 in. beams delay transport 10-15 sec.
- OD rise readily surpasses baseline

## Beam Effect Diminishes at 30 ft. Corridor Width with 18 ft. Height

**Beam Effect Diminishes at 30 ft. Corridor Width with 18 ft. Height**

- For 100kW fire result is comparable to baseline
- Expectation for alarm of baseline detector and postulated detectors with 30 ft. corridor width is low

## Fire Size Key To Detection for Increasing Ceiling Heights 

**Fire Size Key To Detection for Increasing Ceiling Heights **

- For 100kW fire result is comparable to baseline
- Circled data is result for 300 kW fire
- An increased fire size  results in relatively fast rise in OD to levels of expected alarm

## Optical Density – Well Mixed

- These graphics show the traversal soot density distribution at 15’ and 16.5’ from fire, at 60 seconds. The results show that the spaces inside the beam pocket and near the bottom of the beam have comparable soot density gradient.  No stagnant zone is observed near the sidewall or at the corners

## Velocity - (Ceiling Height 12’, Corridor Width 5’, Beam Depth 12”) - 1.5” off wall

## Velocity - (Ceiling Height 12’, Corridor Width 5’, Beam Depth 12”) - 1.5” below ceiling

## Velocity - (Ceiling Height 12’, Corridor Width 5’, Beam Depth 12”) - 1.5” below beams

## Corridor - Basic Findings

**Linear Spacing of Smoke Detection**
- The data observed in this analysis indicates that for ceilings up to 18 feet in height, that deep beam configurations do not negatively affect expected performance.  Reservoir effect contributes to beneficial rise in OD as compared to smooth ceiling scenarios. This means that for these conditions, detector can be effectively used in corridor with deep beams at spaces of 30 to 41 feet as is permitted for smooth ceilings
**Increasing Ceiling Heights**
- As ceiling height increases the fire size threshold needed for activation of the baseline spot smoke detector must increase. With an increased fire size the smoke detectors on a beam ceiling will be comparable to the performance result for the baseline detector at the same ceiling height.
**Location Under Beams/On Ceiling Between Beams**
- Where deep beams interrupt the ceiling surface in a corridor, mounting the detector on the ceiling between beams or the bottom of the beam is acceptable, either location providing comparable response to alarm
**Sidewall Mount or Center of Corridor**
- Keeping smoke detector locations 12 inches below or away from a ceiling-wall corner appears unsubstantiated.  No stagnant zone or locations are observed that would preclude smoke detector alarm.  Temperature and smoke optical density are relatively uniform and well-mixed throughout the volume of the beam pocket within seconds after the initial ceiling jet passes

## Beam Pocket Scenarios

- 	Small rooms:
- 	-	Pocket size 3x3, 6x6, 12x12 ft, and
- 	-	Beam depth of 0 (as baseline), 12, 24 inches, with
- 	-	Ceiling heights of 12, 18, and 24 feet

- 	Large rooms:
- 	-	Pocket size 3x3, 6x6, 12x12 ft, and
- 	-	Beam depth of 0 (as baseline), 12 inches, with
- 	-	Ceiling heights of 36 feet

- 	Fire sizes:
- 	Ceiling height (ft)		Constant Flaming Fire (kW)
- 		12				100
- 		18				200
- 		24				300
- 		36 feet				600kW

## Beam Pocket Model 

## Case – CH 18 ft., BD 24 in., PS 6x6 ft.

- slice in-pocket under ceiling

## Case – CH 18 ft., BD 24 in., PS 6x6 ft.

- slice just under beams

## Optical Density Profile for 3 x 3 ft. Pockets

- OD, H18D24P3, 15 to 30 seconds, 10cm below the ceiling

**Notes:**
Run through this slide quite quickly. All that needs to be said follows:

The purpose of the in-situ tests were to confirm the trends observed on the computer modeling. The performance of various detector technologies under a variety of beam pocket scenarios was tested, using relatively small fire sources in a scaled down, mock-up facility.

A beamed ceiling was constructed where the pocket size and depth could easily be varied. Various tests were conducted with different fire sources and the results noted. Later these results were compared to the computer model (NIST FDS Version 3), to confirm the model’s accuracy.

## Optical Density Profile for 12 x 12 ft. Pockets

- OD, H18D24P12 at 30 seconds

- Near Beam

- Centerline of pocket

- Far Beam

## Temperature Profile for 12 x 12 Pockets

- Temperature, H18D24P12 at 30 seconds

- Near Beam

- Centerline of pocket

- Far Beam

## Case – CH 18 ft., BD 24 in., PS 3x3 ft.

- -5 seconds from baseline for detectors at 15 and 18 foot spacing

- -22 seconds from baseline for detectors at 30 ft. spacing

## Case – CH 12 ft., BD 24 in., PS 6x6 ft.

- -18 seconds from baseline for detectors at  18 foot spacing

- -30 seconds from baseline for detectors at  24 foot spacing

- -40 to 50 seconds from baseline for detectors at  30 foot spacing

## Scenario H12D24P06In the Pocket

**Notes:**
Read slide as is

## Scenario H12D24P06Under the Beam

**Notes:**
Read slide as is

## Case – CH 12 ft., BD 24 in., PS 6x6 ft.

- -8 seconds from baseline for detectors at  24 foot spacing

- -13 seconds from baseline for detectors at  30 foot spacing

## Beam Pockets Data Summary

## Beam Pockets Data Summary

## Waffle or Pan Type Ceilings  Basic Findings

**Linear Spacing of Smoke Detection**
- The data observed in this analysis indicates that for pan type ceilings with beams or solid joists no greater than 24 in. deep, and  beam spacing no greater than 12 ft. center -to-center configurations do not negatively affect expected performance.  Reservoir effect contributes to beneficial rise in OD as compared to smooth ceiling scenarios. This means that for these conditions, detector can be effectively used in waffle or pan type at a spacing of 3o ft.
**Increasing Ceiling Heights**
- As ceiling height increases the fire size threshold needed for activation of the baseline spot smoke detector must increase. With an increased fire size the smoke detectors on a beam ceiling will be comparable to the performance result for the baseline detector at the same ceiling height.
**Location Under Beams/On Ceiling Between Beams**
- Where deep beams interrupt the ceiling surface in a room, mounting the detector on the ceiling in beam pockets or the bottom of the beams is acceptable, either location providing comparable response to alarm for flaming fires
**Sidewall Mount or Center of Beam Pocket**
- Keeping smoke detector locations 12 inches below or away from a beam-ceiling corner appears unsubstantiated.  No stagnant zone or locations are observed that would preclude smoke detector alarm.  Temperature and smoke optical density are relatively uniform and well-mixed throughout the volume of the beam pocket within seconds after the initial ceiling jet passes.

## Thanks for Your AttentionQuestions?