FRAMEWORK DE DESARROLLO PARA J2EE

The heat release rate for the scenario is based on full scale testing that was performed by the National Institute of Standards and Technology as documented in the Figure 3-1.102 of the SFPE handbook. For conservatism, the steady state HRR was modified to 4,000 kW to account for additional fuel packages that would likely ignite and contribute to the severity of the fire.

Chapter 6 – Performance Based Evaluation 6-10

Figure 6-5. Heat release rate of couch (F32) (Ref. 18)

The carbon monoxide yield and soot yield used in this analysis is based on the average soot yields of polyurethane flexible foams as reported in Table 3-4.16 of the SFPE Handbook. Data is

summarized below in

Table 6-1. Reported and average values of CO and soot yield (Ref. 18)

Material YCO [g/g] YSoot [g/g]

GM21 0.010 0.131

GM23 0.031 0.227

GM25 0.028 0.194

GM27 0.042 0.198

Average 0.028 0.188

Table 3-4.16 of SFPE

Heat of combustion and the chemical formulation of polyurethane foam used in Fire Dynamic Simulator (FDS) input file have been obtained from Table C.3 of the SFPE handbook. Polyurethane foam has a heat of combustion of 22.7MJ/kG and a chemical composition of C = 6.3, H=7.1, N=1, and O=2.1.

Chapter 6 – Performance Based Evaluation 6-11 6.4 Tenability Criteria

Tenability criteria need to be appropriate for the occupants and their level of alertness while in the building. RMSEL personnel are awake and the facility is equipped with an automatic sprinkler system and partial coverage smoke detection. For these reasons, occupants are not expected to succumb to effects of toxics, irritants, or asphyxiate.

The presence of smoke detection, smoke control system and an automatic sprinkler system may not be able to control the spread of smoke. Smoke can threaten occupants because it develops early in the fire and impairs the occupant’s visibility. The loss of vision clarity in smoke is

detrimental to egress as occupants become unwilling to travel through it, especially when they are not fully aware of where they are going.

RMSEL’s atrium has the potential to spread smoke between the first and second floors. Given the concerns about smoke, an applicable performance criterion is to limit the smoke layer to a height of 6 ft on the second floor. This criterion is specified in section 909.8.1 of the 2012 IBC when using the exhaust method for smoke control. However, the 1994 UBC required a smoke layer height of 10 ft. Layer heights are not used for this analysis because, despite being required, the system was not designed in that manner. To maintain a layer height, exhaust is generally designed from the top of the compartment with inlets down near the bottom. The RMSEL smoke control system uses the ducting and supply fan for the building HVAC. Supply ducts are located at all elevations of the building meaning they inject fresh air into the smoke layer, which causes the smoke layer to expand. This also disrupts the smoke layer making it uneven and causes it to descend below 6 ft.

A more appropriate performance criterion for RMSEL is visibility. The most conservative value for visibility discussed in the SFPE handbook is 13 m. Thirteen meters is good for buildings where the occupants are not familiar with the layout of the building. Since RMSEL host visitors, this seems appropriate. Another reason for using visibility is the fact that FDS has been shown to predict visibility well has a model bias factor of 1.01, meaning FDS tends to over predicts visibility by 1%. FDS does a poor job of predicting smoke concentration as it over predicts by

approximately 260%. See the following figures for more information.

Chapter 6 – Performance Based Evaluation 6-12

Figure 6-6. FDS model bias for visibility (Ref. 20)

Figure 6-7. FDS model bias for smoke concentration (Ref. 20)

Chapter 6 – Performance Based Evaluation 6-13 6.4.1 Results

An important aspect of this fire scenario is to characterize the benefit of the smoke control system.

To do this, four scenarios were evaluated: 1) unmitigated (i.e, no sprinklers or smoke control), 2) sprinklers only, 3) smoke control only, 4) sprinklers and smoke control. Sprinklers were

simulated by determining the activation time using the heat detectors in the unmitigated model and capping the HRR in the runs with sprinklers.

Figure 6-8. HRR used in the fire models

FDS slice files showing the visibility at locations sensitive to evacuation are shown in Figures 6-9 through 11 for the unmitigated scenario and Figures 6-12 through 15 for the sprinkler and smoke control case.

Chapter 6 – Performance Based Evaluation 6-14

Figure 6-9. Unmitigated - loss of visibility at conference room

Figure 6-10. Unmitigated - loss of main entrance egress

Chapter 6 – Performance Based Evaluation 6-15

Figure 6-11. Unmitigated - loss of tenability at NE stairwell

Figure 6-12. Sprinkler controlled –loss of tenability at 2^nd floor conference room

Chapter 6 – Performance Based Evaluation 6-16

Figure 6-13- Sprinkler controlled - loss of tenability at main entrance

Figure 6-14. Sprinkler controlled - loss of tenability at NE exit

Chapter 6 – Performance Based Evaluation 6-17 Despite the presence of the smoke control system and sprinklers, tenability is lost throughout the atrium. However, the smoke control does help extend the time it takes to loose tenability. Times associated with the loss of tenability need to be put into context with respect to the evacuation times. This analysis is generally referred to as a comparison of the required safe egress time (RSET) and the available safe egress time (ASET). The RSET has to been less than the ASET SFPE handbook defines RSET as

RSET = t

+ t

+ t

+ t

where td = time from ignition to detection tn = time from detection to notification tp-e = time from notification to evacuation commences

te = time to evacuate once evacuation commences.

The unmitigated scenario showed sprinklers or a heat detector would take approximately 100 seconds from the time the fire started to the time of detection. For the analysis, the detector is assumed to have a 74°C (165°F) activation temperature and a response time index of 105 (ms)^1/2. Therefore, td = 100 seconds.

For this analysis, two times are considered for the time from ignition to detection. The first assumes the detection is smoke detectors, which has a rapid notification time. For this case, td is assumed to be zero. In the case of sprinkler flow, a 60 sec delay is assumed because this is the maximum allowable delay time allowed by the code.

The occupants are awake and alert. These are important aspects to consider when estimating the time it takes for the occupants to actively start removing themselves from the building. However, the Sandia performs numerous evacuation drills and exercises and because Sandia has a fair number of nuisance alarms, it is assumed that it will take the occupants roughly 60 seconds to start moving once they are aware of the alarm. Therefore, tp-e is 60 seconds

This analysis will evaluate loss of tenability at four distinct locations. The first is the second floor conference room located on the north end of the atrium. The second is the main entrances near the north of the corridor. The third location is the northeast stair well and the final location is the central west exit. The RSET values for each of these locations is compared to the ASET values in Table 6-2.

Chapter 6 – Performance Based Evaluation 6-18

Table 6-2. RSET vs ASET results*

Location RSET**

(heat

detectors/sprinklers) [seconds]

ASET [seconds]

Unmitigated Mitigated –

sprinklers only

Mitigated – smoke control

only

Mitigated – Sprinklers and Smoke Control 2^nd floor conference

rm

190/250 73 93 106 127

Main entrance 210/270 104 106 125 127

2^nd floor east stairwell 220/280 134 137 180 247

Middle corridor 220/280 220 286 292 338

South exit 225/285 352 424 398 560

*Numbers in bold lettering indicate

**The difference between heat detectors and sprinklers is the assumption that heat detectors notify immediately and sprinklers notify after a 60 second delay.

Chapter 7 – Summary and Recommendations 7-1