What is the water delivery time?
When dry or pre-action systems are installed, the network is air pressurized. When activated, the control valve releases the water upon thermal activation of the sprinkler i.e. when the fire is already spread. The water delivery time is the time it takes to simulates or observe the delivery of the water through an inspector test connection that simulate the orifice size of a single or several sprinklers on the system
What are the requirements within NFPA 13?
There are different requirements depending on the size of the system. When related to the size, it means the volume of the dry system.
Volume | What is need for having nowater delivery time requirement |
0-1900 liters 0-500 gpm | No requirement at all |
0-2900 liters 0-750 gpm | No requirement if presence of a quick opening device |
It is often discussed even by experienced risk engineers if it is acceptable to have a water delivery time greater than 60 seconds for systems less than 1900 liters (500 gal) in size that are not protection dwelling units.
It has been considered and ELEN RISK CONSULTING considers it fair, that it was important to have a rule that allows small dry pipe system to be installed without requirement regarding the water delivery time. If the time is above 60 seconds, it is difficult for the contractor to do anything about this situation at that point since the system is already installed.
Some risk engineers may ask the installing of a quick opening device but does it really improve the installation requirements when not paying attention to the slope, corrosion issue etc.
Is the size of the dry pipe system the only information needed?
No, it is not.
Hazard | Number of most remot sprinklers initially open | Maximum time of water delivery (seconds) |
Light | 1 | 60 |
Ordinary | 2 | 50 |
Extra | 4 | 45 |
High pilled | 4 | 40 |
This table represents the anticipated minimum number of the most remote sprinklers initially open in the early stage of fire growth. Fires with a higher heat release are expected to activate greater number of sprinklers. It makes sense knowing that the more hazardous the occupancy is, the lower the area covered by a sprinkler is.
The reduction in time is due to the number of open sprinkler. This has been justified to more closely represent the actual performance of a dry sprinkler in response to fires.
What are the key factors to consider for a water delivery time test?
It is very important to ensure that the inspector test connection is well designed. Indeed with High Pilled hazards, the number of most remote sprinklers initially open increase up to 4 while the maximum time of water delivery decreases dramatically from 60 sec to 40 sec.
If the ITC is calculated for one single sprinkler head, it is therefore very complicate for the water delivery time to respect the 40 sec requirement. Remind that the maximum time of water delivery for EH or HP occupancies is a conservative reduction in time from the 60 second criteria for a single sprinkler in light hazard. With the heat release of these hazards, four sprinklers activate in a short period of time. The result is a more accurate delivery time to simulate the real world event of activation sequence, allowing the system to deliver water sooner than 60 seconds
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