help!how long of response time for the fire water spray system?

[driftshade]

according to NFPA 15-2007 ,The response time for the system required as following:
   " the system and water supplies shall be designed to admit water into the piping and to discharge effective water spray from all open nozzles without delay"
        i have two questions of this regulation:
   1.does the response time account from the fire pump receiving the start-up signal to the fire water flowout of  the furthest nozzle?
   2.how long of the response time?

[John Webb]

I've not got access to the NFPA15-2007 document and I must admit have not dealt with such systems for some years. What I think the NFPA document is trying to ensure that there is no deliberate delay between the sensing of the fire and the application of water. For example, if the sensor is an electric detector the occupier might try and argue that they ought to have time to investigate the alarm in case it is false.

So the NFPA wording says, in effect "get the water flowing as soon as the fire is sensed".

It also means that the system needs to be designed so that the pump has adequate capacity to fill the pipes, that the pipes are not too long and therefore can be filled reasonably quickly, and that the water supply can cope with the initial surge when the pipes are being filled. As to time-scale, it does depend on the risk present, but I would have thought a half to one and a half minutes was a reasonable target - others more up to date may have other views.

[wee brian]

Alternatively it could mean that the system is kept under pressure with a jockey pump.That way you dont have to wait for the main pump to wind itself up.

If I'm standing next to a petrochem plant with flames coming out of it and I hit the panic button, I dont want to wait a minute or so for the drenchers to work (I'm running for my life at that stage.

Its not a very helpful clause in a standard but hey, US standards are always a bit random.

[Midland Retty]

As wee Brian suggests the use of jocket pumps and panic buttons should be used in places where

a)The scenario Wee Brian already gives whereby a human is able to detect a fire quicker than a detector does

b) the investigation of alarm activations form part of the fire strategy - so in other words and as an example imagine a security guard at a firm whom investigates all fire alarm activations. He is alerted to an activation in an area protected by water mist.

The guard verifies it is a false alarm, and radios back to his control room to cancel activation of spray system remotely, or on the other hand confirms that it is a genuine activation and is either able (from a position of safety) to manually operate the water mist before it kicks in, or radio through to colleagues to operate it from a central control room  

Crude examples but hopefully you get the gist.

[driftshade]

thanks for all the replies. in my opinion ,the response time for the fire water spray sytem required in NFPA 15 is just contrapose to the auto-start scenario on the assumption that :
            1.there was a fire indeed;
            2.the system works normally;
            3.avoid the human factors and extreme environment condition exceed the design considration,sucn as ice,earthquake,war and so on.

    let's take a fire water spray system on the offshore platform as a example,if there's a fire on some fire zone on the platform,the fire water system will works as followng process:
             1.there's a fire on some place,
             2.the flame detectors detect the fire,and send the signal to the Fire and Gas Control Panel
             3.the fire and gas control system verifies the fire
             4.a serials of instructionsends out to open the deluge valve and firewater pump
             5. after the deluge valve was open,the firewater used to keep pressure of firemain flows out,at the same time,the firewater pump is being started,10 seconds approximately,the fire pump will achieve rating work point ,15 seconds approximately after the deluge valve opened,the furthest nozzle will spray fire water.

            but we also have another type fire water system,we call it dry system,normally,there's no water in the fire pipe net to keep the pressure,
so after the fire pump started and the deluge valve opened,it will take periods of time to fill the fire water to the pipe net,and the electric start also will take 10 second,it's a long time ,so we want to know?how long response time the NFPA 15 required in order to verify our system feasability.

[John Webb]

Driftshade,
I did wonder from your first post when you spoke about "water being admitted to the piping" if you were talking about a dry system. Your personal details don't tell us where you are writing from. If in the USA I'd try ringing NFPA, if outside I'd try e-mailing them to ask them directly if they have any particular time period in mind.

[driftshade]

thank you ,i am so sorry not give the detail information.but i think no matter wet system or dry system,they both are fire water system,the response time is a problem shall be considered .
note:
    the dry sysem means there's no water on the pipe net in normally condition .
    the wet system means there's water on the pipe net between the check valve on the fire pump discharge pipe to the upstream of deluge valve, or ohter case to the closed nozzle in normally condition.