The investigated parameters are:
- Room properties: Room area, ceiling height and thermal properties of materials
- Sprinkler properties: RTI, activation temperature and distance sprinkler head from ceiling
- Fire properties: Growth rate and heat release per unit area.
A summary of the results is presented in the table below. Detailed properties and results of the simulations for each investigated parameter are presented in the slider at the bottom of the page.
Most relevant results are:
For residential applications the room size and fire growth rate both highly influence the sprinkler activation time.
In small rooms such as a hotel room of 9 m2 the sprinkler activation time is only 138 s with a heat release rate of 212 kW. For a larger room such as a small apartment of 56 m2 the sprinkler activation time has already increased to 174 s with a heat release rate of 336 kW, which is 58% higher.
The fire growth rate results in a shorter sprinkler activation time but increases the corresponding heat release rate significantly. The sprinkler bulb temperature lags behind the smoke temperature. Hence, when the bulb of the sprinkler has reached its activation temperature a fast growing fire has already grown to a higher heat release rate compared to a medium growing fire. For CFD analysis a faster fire growth is often used to speed up the calculation time and this approach can lead to an overprediction of the heat release rate at sprinkler activation. When using a fast growing fire instead of a medium growing fire (medium room size), the heat release rate at sprinkler activation increases from 336 to 472 kW, which is 40% higher. Note that when comparing a medium growing fire in a 9 m2 room to a fast growing fire in a 56 m2 room the heat release at sprinkler activation increases from 212 kW to 472 kW which is 223% higher.
Properties of the sprinkler head are also relevant. Lower RTI and activation temperatures obviously lead to a shorter activation time. The effect on the heat release rate is even bigger since fire growth models assume a quadratic fire growth in time.
Another very important factor is the distance from the ceiling to the sprinkler head. Especially for large rooms where no smoke layer is built up, the sprinkler activation time is extended significantly with sprinkler heads further away from the ceiling.
Properties held constant:
-Sprinkler: RTI 80 m0.5s0.5, 77 °C activation temperature, 10cm from ceiling at 3m spacing
-Room: Height 2.4 m, Plasterboard
-Fire: Medium fire growth, 250 kW/m2
Effect on sprinkler activation time:
The room area affects the sprinkler activation time significantly. The smoke layer height drops faster due to the smaller volume available for smoke. In small rooms such as a hotel room of 9 m2 the sprinkler activation time is only 138 s with a heat release rate of 212 kW. For a larger room such as a small apartment of 56 m2 the sprinkler activation time has already increased to 174 s with a heat release rate of 336 kW, which is 58% higher. For very large rooms the sprinkler activation time has increased to 262 s or 763 kW.
Properties held constant:
-Sprinkler: RTI 80 m0.5s0.5, 77 °C activation temperature, 10cm from ceiling at 3m spacing
-Room: Area 56 m2, Height 2.4 m, Plasterboard
-Fire: 250 kW/m2
Effect on sprinkler activation time:
A faster growing fire results in a shorter sprinkler activation time but increases the corresponding heat release rate significantly. The sprinkler bulb temperature lags behind the smoke temperature. Hence, when the bulb of the sprinkler has reached its activation temperature a fast growing fire has already grown to a higher heat release rate compared to a medium growing fire. Increasing the fire growth rate from medium to fast increases the heat release rate at sprinkler activation from 336 to 472 kW, which is 40% higher.
Properties held constant:
-Sprinkler: RTI 80 m0.5s0.5, 77 °C activation temperature, 10cm from ceiling at 3m spacing
-Room: Area unlimited (open sides), Plasterboard
-Fire: Medium fire growth, 250 kW/m2
Effect on sprinkler activation time:
The heights of 2.4 and 3.5 m apply to residential buildings. Increasing the ceiling height from 2.4 m to 3.5 m increases the sprinkler activation time from 277 s to 313 s, which translates to an increase in heat release rate of 853 kW tot 1089 kW
Properties held constant:
-Sprinkler: RTI 80 m0.5s0.5, 77 °C activation temperature, 10cm from ceiling at 3m spacing
-Room: Area 56 m2, Height 2.4 m
-Fire: Medium fire growth, 250 kW/m2
Effect on sprinkler activation time:
The influence of the materials used on the sprinkler activation time is limited. However, there is a small reduction of the sprinkler activation time with lower thermal conduction to the walls and ceiling.
Properties held constant:
-Sprinkler: 77 °C activation temperature, 10cm from ceiling at 3m spacing
-Room: Area 56 m2, Height 2.4 m, Plasterboard
-Fire: Medium fire growth, 250 kW/m2
Effect on sprinkler activation time:
As expected a more sensitive sprinkler head with lower RTI results in a faster sprinkler activation time. An increase in RTI from 50 to 200 m0.5s0.5 increases the sprinkler activation time from 162 s to 204 s, or from 292 kW tot 460 kW, which is 57% higher.
Properties held constant:
-Sprinkler: RTI 80 m0.5s0.5, 10cm from ceiling at 3m spacing
-Room: Area unlimited (open sides), Height 8.0 m, Plasterboard
-Fire: Medium fire growth, 250 kW/m2
Effect on sprinkler activation time:
Similar to a more sensitive sprinkler (lower RTI) a sprinkler with a lower activation temperature results in a faster sprinkler activation time. An increase in sprinkler activation temperature from 57 to 77 °C increases the sprinkler activation time from 256 to 336 s, or from 728 kW to 1251 kW, which is 72% higher. Increasing the sprinkler activation temperature even further to 93 °C increases the sprinkler activation time to 384 s, 1638 kW. Note that a large room height was used for this investigation to mimic high spaces such as atria or warehouses.
Properties held constant:
-Sprinkler: RTI 80 m0.5s0.5, 77 °C activation temperature
-Room: Area unlimited (open sides), Height 8.0 m, Plasterboard
-Fire: Medium fire growth, 250 kW/m2
Effect on sprinkler activation time:
The distance of the sprinkler head to the ceiling has a huge effect on the sprinkler activation time. Increasing the distance from 0.1 to 0.3 m increases the sprinkler activation time from 387 to 595 s, or 1660 to 3934 kW, which is 237% higher. Note that this type of room is rare, but could be found in production facilities.
Properties held constant:
-Sprinkler: RTI 80 m0.5s0.5, 77 °C activation temperature, 10cm from ceiling at 3m spacing
-Room: Area 56 m2, Height 2.4 m, Plasterboard
-Fire: Medium fire growth
Effect on sprinkler activation time:
The influence of the heat release rate per unit area on the sprinkler activation time is limited. However, there is a small reduction of the sprinkler activation time with higher heat release rate per unit area. Increasing the heat release rate per unit area from 250 to 500 kW/m2 decreases the sprinkler activation time from 174 to 158 s, or 336 to 276 kW, which is 18% lower.
