3.1 Building Temperature Measurements
The 0.9 m above the floor (crawling height) temperature was used to assess the thermal exposure to which an occupant trapped at different locations within the structure may be subjected. The average temperature in the 30 s prior to firefighter intervention in the hallway, outside of the fire rooms was
\(320 \pm 64^{\circ }\hbox {C}\). In the dining room, remote from the seat of the fire, the average temperature was
\(135 \pm 34^{\circ }\hbox {C}\). The coefficients of variance were 20% and 25% for the hallway and dining room locations, respectively. These values are greater than the combined instrument uncertainty of 15%, a difference which can partially be attributed to the wind. Since the test structure was not located in a controlled lab space, the presence or absence of wind could have an effect on flow paths within the structure. The wind conditions are shown in Table
2. Winds gusted as high as
\(7.3\ \hbox {m}/\hbox {s}\) during Experiment 5 however did not average more than
\(3.2\ \hbox {m}/\hbox {s}\) in any of the experiments. The 0.9 m above the floor temperatures measured in the closed bedrooms were significantly lower than those measured in the areas of the structure open to the fire. The average temperature in the 30 s prior to intervention was
\(23 \pm 2^{\circ }\hbox {C}\) in the near bedroom and
\(21 \pm 1^{\circ }\hbox {C}\) in the far bedroom. The coefficient of variation for these sensors are 7.0% and 5.8% for the near and far bedrooms, respectively, less than the 15% combined uncertainty of the thermocouples. Representative temperature versus time graphs for each room and occupant locations are included in [
13].
Table 2
Wind Speed (m/s) and Direction
Exp. 1 | 2.8 | 0.6 | 6.9 | W |
Exp. 2 | 2.6 | 0.2 | 6.0 | SW |
Exp. 3 | 1.9 | 0.1 | 5.3 | NE |
Exp. 4 | 0.9 | 0.0 | 2.0 | SE |
Exp. 5 | 3.2 | 0.5 | 7.3 | SW |
Exp. 6 | 1.5 | 0.0 | 5.3 | NW |
Exp. 7 | 1.0 | 0.0 | 2.7 | W |
Exp. 8 | 1.6 | 0.0 | 5.9 | NW |
Exp. 9 | 1.7 | 0.1 | 4.8 | NW |
Exp. 10 | 2.0 | 0.0 | 5.2 | SW |
Exp. 11 | 1.2 | 0.0 | 3.3 | W |
Exp. 12 | 1.2 | 0.0 | 3.2 | W |
The high temperatures at 0.9 m above the floor in the open areas of the structure resulted in
\(\hbox {FED}_{temp}\)s in the hallway that exceeded the criteria for second degree burns. In the interior attack experiments, an
\(\hbox {FED}_{temp}\) exceeding 1.0 was reached in
\(322 \pm 48\ \hbox {s}\) and was reached in
\(322 \pm 34\ \hbox {s}\) during the transitional attack experiments. For each attack method, this value was reached prior to firefighter intervention (
\(442 \pm 24\ \hbox {s}\) for interior and
\(399 \pm 16\ \hbox {s}\) for transitional). The maximum FEDs for each experiment and simulated occupant location are listed in Table
3. At the dining room simulated occupant location distant from the fire rooms, only Experiments 1 and 2 reached a
\(\hbox {FED}_{temp}\) in excess of 1.0. For the other experiments, the FED at the end of the experiment was
\(0.69 \pm .17\) for the interior attack experiments and
\(0.62 \pm .30\) for the transitional attack experiments.
The least severe thermal conditions were observed in the two closed bedrooms where temperatures at the time of firefighter intervention were lower in both locations than in the areas immediately outside of the closed door. Once firefighter intervention was initiated, whether from the interior or the exterior, there was no immediate effect on the temperatures or
\(\hbox {FED}_{temp}\) within the room. In the experiments where the closed bedroom doors were opened for search and rescue, however, there was a corresponding temperature increase and
\(\hbox {FED}_{temp}\) rate increase. Although opening the bedroom door to facilitate search often resulted in a measurable increase in the
\(\hbox {FED}_{temp}\) rate, the total FED in both closed bedrooms remained below 0.10 for both bedrooms and the 0.9 m above the floor temperature never exceeded
\(40^{\circ }\hbox {C}\). Even the most severe thermal conditions within the bedrooms to which a trapped occupant would be subjected were less severe than those encountered in areas of the structure connected to the fire rooms.
Table 3
Final FEDtemp Values at Each Measurement Location
Exp. 1 | 7.92 | 1.28 | 0.02 | 0.01 |
Exp. 2 | 12.02 | 3.25 | 0.04 | 0.04 |
Exp. 3 | 9.69 | 0.87 | 0.04 | 0.03 |
Exp. 4 | 35.43 | 0.56 | 0.02 | 0.03 |
Exp. 5 | 33.25 | 0.76 | 0.07 | 0.03 |
Exp. 6 | 8.86 | 0.24 | 0.03 | 0.02 |
Exp. 7 | 16.64 | 0.68 | 0.03 | 0.02 |
Exp. 8 | 9.15 | 0.29 | 0.02 | 0.03 |
Exp. 9 | 39.07 | 0.43 | 0.04 | 0.03 |
Exp. 10 | 1.96 | 0.43 | 0.03 | 0.03 |
Exp. 11 | 19.76 | 0.86 | 0.04 | 0.03 |
Exp. 12 | 7.97 | 0.71 | 0.03 | 0.04 |
3.2 Building Gas Concentration Measurements
At the time of firefighter intervention, the FED calculations varied considerably between experiments. At the near hallway location, just outside of the bedroom fires, the average FED value at the time of firefighter intervention was
\(1.06 \pm 0.96\). In the dining room location, next to the first simulated occupant, the average FED was
\(0.34 \pm 0.36\). The coefficients of variation were higher than those calculated for the building temperatures, and were 90% and 105% for the hallway and dining room, respectively. The variation that was noted in these measurements can be attributed to variations in the CO,
\(\hbox {CO}_2\), and
\(\hbox {O}_2\) measurements. The variation in these measurements was greater than the uncertainty of the sensors. Additionally, because the FED equations presented in Eqs.
2 and
3 are exponential in nature, small measurement variations will result in larger variations in the FED calculation. Further, ISO 13571 [
12] lists the uncertainty for the FED calculations as high as 35%. In the closed bedrooms, the average FED value at the time of firefighter intervention was
\(0.007 \pm 0.005\).
Incapacitation levels were reached at
\(467 \pm 67\ \hbox {s}\) and
\(453 \pm 31\ \hbox {s}\) in the hallway gas sample location for the transitional and interior attacks, respectively. On average, the dining room occupant location reached incapacitating levels of exposure at a later time than the hallway, at
\(533 \pm 78\ \hbox {s}\) and
\(618 \pm 136\ \hbox {s}\) from ignition, for the transitional and interior attack, respectively. These times occur after the average firefighter intervention times (
\(390 \pm 16\ \hbox {s}\) for transitional attack,
\(442 \pm 24\ \hbox {s}\) for interior attack). Table
4 lists the maximum FEDs observed for each measurement location in each experiment. The average total FED values for the locations open to the fire rooms were
\(3.08 \pm 1.17\) and
\(2.31 \pm 1.03\) for the near hallway and dining room locations, respectively. These values were substantially higher than the FEDs recorded in the closed bedrooms, which were
\(0.63 \pm 0.58\) and
\(1.09 \pm 0.54\) for the near and far closed bedrooms, respectively. There was no significant difference between the two bedrooms (
\(p=0.22\)). This indicates that the closed bedroom door can provide an important reduction in an occupants exposure to products of combustion, which are noted in high concentrations low to the floor in the open areas of the house. Even in the near closed bedroom, the FED values measured behind the closed door are significantly lower (
\(p=0.005\)) than in the hallway immediately outside the bedroom. The near bedroom sample point was also significantly lower (
\(p=0.003\)) than the sample point located in the dining room, next to the simulated occupant. Representative gas concentration versus time graphs for each sample location are included in [
13].
Table 4
Final FEDgas Values at Each Measurement Location
Exp. 1 | n.a | 4.62 | 0.51 | 0.19 |
Exp. 2 | 3.31 | n.a | 0.45 | 1.08 |
Exp. 3 | 4.13 | 3.26 | 1.64 | 0.55 |
Exp. 4 | 1.85 | 1.00 | 0.14 | 2.38 |
Exp. 5 | 3.58 | 1.39 | 1.89 | 1.13 |
Exp. 6 | 2.27 | 1.68 | 0.43 | 1.04 |
Exp. 7 | 4.19 | 2.44 | 0.83 | 0.83 |
Exp. 8 | 1.91 | 1.75 | 0.62 | 1.43 |
Exp. 9 | 2.86 | 1.90 | 0.31 | 1.06 |
Exp. 10 | 1.26 | 1.59 | 0.09 | n.a |
Exp. 11 | 5.42 | 3.50 | n.a | 1.17 |
Exp. 12 | 3.05 | 2.27 | 0.07 | n.a |
3.3 Firefighter Intervention Measurements
Each group of firefighters participated in one transitional attack experiment and one interior attack experiment. The only direction given to the groups performing these tasks was which method of attack to perform and which direction the search team should begin their search. A considerable amount of variation was noted in the time that the various groups took to complete fireground tasks such as hoseline deployment, hoseline advancement, and occupant location and removal. Table
5 lists the average times (with standard deviations) that the groups took to perform these actions. The least amount of variation (defined by the coefficient of variation), approximately 20%, was noted in the hoseline deployment, which was defined as the time that the firefighter removed the hoseline from the fire engine to the time that the nozzle was “bled,” ensuring that the attack team had a serviceable hoseline with water to the nozzle. The variability in the hoseline advancement, which was defined as the time from when the attack team entered the door to when they reached the hallway, was higher at 55%. The highest variability was noted in the forcible entry task, which was 95%.
Table 5
Times for Firefighting Tasks
Hoseline deployment |
\(79 \pm 16\)
| 20 |
Hoseline advancement |
\(29 \pm 16\)
| 55 |
Forcible entry |
\(22 \pm 21\)
| 95 |
Time to locate dining room occupant |
\(48 \pm 22\)
| 35 |
Time to remove dining room occupant |
\(37 \pm 13\)
| 45 |
Time to locate bedroom occupant |
\(140 \pm 54\)
| 39 |
Time to remove bedroom occupant |
\(60 \pm 38\)
| 63 |
The timeline of firefighter interventions varied with both the method of attack (transitional vs. interior) and the actions taken by the subjects during their execution of the fire attack (Table
1). From the time that the hoseline was pulled from the engine, the transitional attack resulted in significantly faster water application to the fire (
\(p<0.001\)) than the interior attack method. For the transitional attack, water was applied to the front bedroom in
\(82 \pm 9~\hbox {s}\), whereas in the interior attack experiments, entry to the structure was made in an average of
\(127 \pm 11\ \hbox {s}\) after pulling the hoseline. Most of the interior attack teams utilized a “shut down and move” technique, where water would be applied from a stationary position, before advancing and repeating the maneuver. The teams applied water sometime between entering the structure and reaching the hallway. The first interior water application occurred
\(10 \pm 6\ \hbox {s}\) following entry, and most teams applied water for
\(3 \pm 2\ \hbox {s}\) on this initial application.
The average time between dispatch and entry for the search company was
\(204 \pm 24\ \hbox {s}\) for the interior attack experiments and
\(227 \pm 29\ \hbox {s}\) for the transitional attack experiments, which was not significantly different (
\(p=0.21\)). The longer average entry time in the transitional attack experiments was attributed to the additional time required to reposition the line to make entry in these experiments. In Experiments 1, 5, 7, and 8, the search teams missed the far closed bedroom, and the door was never opened. Table
6 shows the average times for the search team to find and remove each occupant during each fire attack method. While there is large variability in each of these times, method of attack (and its subsequent impacts on visibility and thermal conditions) was found to not have a significant difference on the time required to find the dining room occupant (
\(p=0.75\)) or the bedroom occupant (
\(p=0.32\)). Similarly, time required to remove the dining room occupant (
\(p=0.38\)) and bedroom occupant (
\(p=0.85\)) was not found to be significantly different between attack methods.
Table 6
Times to Find and Remove Occupants
Time to find dining room occupant |
\(36 \pm 15\)
|
\(38 \pm 10\)
|
Time to remove dining room occupant |
\(42 \pm 21\)
|
\(54 \pm 21\)
|
Time to find bedroom occupant |
\(218 \pm 62\)
|
\(264 \pm 74\)
|
Time to remove bedroom occupant |
\(50 \pm 64\)
|
\(56 \pm 21\)
|
As the search company opened the doors to the near and far bedrooms in order to gain access and complete their search, the bedroom was no longer isolated from the rest of the structure. Out of the twelve experiments, eight search teams made entry into the far closed bedroom and searched it, and four passed over the bedroom, leaving the door closed and not searching. In the cases where the remote bedroom was opened and searched, an increase in FED rate was observed as products of combustion filled the room. For the four tests in which the door was not opened during the initial part of the search, this increase in FED rate was not observed. The peak FED rate calculated in the experiments where the search team opened the door (\(0.0030 \pm 0.0010\)) was significantly higher (\(p=0.003\)) compared to the peak FED rate for experiments where the door to the far closed bedroom was not opened and searched (\(0.0010 \pm 0.0002\)). For the far closed bedroom, which was opened and searched earlier in the timeline of the experiment, opening the door resulted in an increase in the FED rate for any potential occupants located in the room.
The significant increase in FED rate following the opening of the door to the far bedroom was not observed in the near bedroom. The near bedroom door was opened in all twelve of the experiments. There was no significant difference between the maximum FED rate prior to and following the search team’s entrance of the near closed bedroom. This is likely due to this room being opened later into the experiment after suppression had taken place and ventilation was occurring.
When considering the impact of suppression on occupant tenability within the structure, Experiments 3 (transitional) and 5 (interior) were treated as outliers, and neglected from the comparisons. In Experiment 3, the attack team applied water for only 4s in each window, which allowed the fire to regrow by the time that the interior teams entered the structure. In Experiment 5, when the attack team reached the hallway, they did not have a sufficient length of hose to apply water into the fire rooms, reducing the effectiveness of the attack.
For the other experiments, after water was applied, whether from the interior or the exterior, the FED rate in open areas of the structure began to decrease. For the gas sample location in the hallway outside of the fire rooms, this inflection point occurred
\(43 \pm 28\ \hbox {s}\) from the time that water was first applied for the transitional attack experiments and
\(35 \pm 30\ \hbox {s}\) from the time that the attack team made entry for the interior attack experiments (
\(p=0.73\)). For the gas sample location in the dining room, this inflection point occurred
\(100 \pm 43\ \hbox {s}\) from the time that water was first applied for the transitional attack experiments and
\(27 \pm 24\ \hbox {s}\) from the time that the attack team made entry for the interior attack experiments. This difference may not be statistically significant, but may be important in a real fire ground scenario. Apart from the two outliers experiments discussed previously, the FED rate did not increase at any time following water application. Thus, this FED rate inflection point can be taken as the time at which conditions would start to improve for occupants in an areas of the structure not isolated by a closed door or other barrier. For the near hallway position, there was no significant difference between attack methods, but for the dining room location, the interior attack method did improve conditions significantly more rapidly than the transitional attack method (
\(p=0.02\)). A possible reason for the more rapid improvement in the interior attack case is the ventilation that accompanies the opening of the front door and line advancement. As a flow path through the front door is established and fresh air enters the structure, products of combustion are displaced. The entrainment of fresh air, accompanied by the ongoing suppression, likely work in tandem to result in the improvement of conditions remote from the fire room. Table
1 shows that in the transitional attack experiments, water was applied to the fire approximately 45 s sooner after dispatch. The time from dispatch until the
\(\hbox {FED}_{gas}\) rate inflection is
\(205 \pm 36\ \hbox {s}\) for interior attack and
\(169 \pm 24\ \hbox {s}\) for transitional attack, which is not a significant difference between the experiments (
\(p=0.14\)). Similarly, in the dining room sample location, the time from dispatch to the inflection point was
\(225 \pm 46\ \hbox {s}\) for transitional attack and
\(192 \pm 12\ \hbox {s}\) for interior attack, a difference which is also not significant (
\(p=0.27\)). Thus, while the interior attack resulted in a more rapid improvement in conditions in the dining room location from the time of water application, it also took longer from the time of dispatch to apply water to the fire, resulting in no significant difference when considering the two attack methods from a common time frame. There were a relatively small number of replicates and this difference may be important in practice even if not statistically significant.
Similarly, following the application of water, temperatures decreased throughout the structure at the 0.9 m elevations, and continued to decrease for the remainder of the experiment. Temperatures gradually approached ambient as spot fires were extinguished and ventilation was provided. In order to evaluate the effectiveness of the suppression mode, a 60 s window after the time of initial firefighter intervention was examined. This window encompasses the time required to position the hoseline to apply water to both bedroom fires, and captures the highest rate of temperature decrease following suppression. In the hallway between the fire rooms, this temperature decrease was \(261 \pm 101^{\circ }\hbox {C}\) for the transitional attack experiments and \(313 \pm 69^{\circ }\hbox {C}\) for the interior attack experiments, which was not significantly different between the two attack experiments (\(p=0.42\)). The maximum rate of decrease, however, occurred more quickly (\(p=0.004\)) after suppression for the transitional attack (\(8 \pm 4\ \hbox {s}\)) than for the interior attack (\(33 \pm 8\ \hbox {s}\)). This is likely because the limited visibility and geometry hinders the interior attack, an obstacle which is not present in the transitional attack.
The temperatures in the dining room area distant from the fire rooms also improved following suppression, although a larger decrease in temperature was noted for the interior attack than for the transitional attack. For the interior attack method, the temperature decrease was \(103 \pm 29^{\circ }\hbox {C}\) compared to a \(30 \pm 16^{\circ }\hbox {C}\) decrease for the transitional attack (\(p=0.004\)). While this temperature difference is significant, the time between firefighter intervention and the time the minimum FED rate was observed (\(29 \pm 19\ \hbox {s}\) for transitional attack experiments and \(13 \pm 8\ \hbox {s}\) for the interior attack experiments), was not significant. Thus, while the time at which the temperature rate of change begins to decrease rapidly is not significantly different between the two attack methods, the magnitude of this rate difference is more pronounced for the interior attack method. Again, this is likely due to the fact that during the interior attack, the opening of the front door provides an immediate access route for fresh air to enter the structure and hot gases to exit, unlike the transitional experiment where there is no established inlet for fresh air other than the bidirectional flow path at the window until the team transitioned to the front door and opened it. The entrainment of fresh air, combined with the water application of the attack team, may be responsible for the more rapid decrease in FED rate and temperature. In the transitional attack, the opening of the front door was delayed until the attack team has repositioned, so the positive effects of suppression are delayed until ventilation is provided.