NFPA 15 - Effective water spray within 30 seconds after detection

[MikeBP]

Hi,

I work as a technical safety engineer in the oil and gas industry and are trying to find the reason behind the NFPA 15 requirement for effective water spray within 30 seconds after detection as this is very hard target to meet for big offshore installations with large fire pump (longer run-up time). In the latest NFPA 15 the reason behind the requirement is not mentioned other than "needed to meet design objectives". In older revisions of the standard it is mentioned that this is in order to ensure that the system operates (exposure protection) before the formation of carbon deposists on the surfaces to be protected and before the possible failure of any containers of flammable liquids or gases because of the temperautre rise. But I cannot find where the scientific reasoning behind the number "30 seconds". Does anybody know?

Best regards,
Mike

 

[LCREP]

Probably went like this.......10 guys sitting in a committee meeting trying decide how long should the system take to put water on the fire after the detection device activated.

Committee Members

Fire Department Rep....20 secs
Insurance Rep 45 secs
Industrial User...1 min
Fire Detection Rep ...30 secs

They discuss for 3 hours have several votes none coming to a consensus .....almost time for lunch they decide on 30 secs.....take a vote it passes....

I was on a NFPA committee and have witnessed this happen on several occasions.....when you have a consensus standard this is what happens....

 

[MikeBP]

Thanks LCREP for your quick reply!

Yeah your story of how it could have happend is exactly what I am afraid of. The reason why I ask is because reaching that target of 30 seconds is really hard (and costly) when you have big offshore innstallations with very large pumps (20seconds run up time) and big fire areas which means a lot of piping/nozzles to be filled with water. As of this I would like to challenge this requirement. If having effective water spray within (as an example) 45 seconds in stead of 30 seconds have little impact on the fire scenario (needs to be documented) then that would simplify design and costs to a very high degree. Because of this any scientific reason behind the 30 seconds would be nice to know.

 

[LCREP]

Mike,

Have you contacted NFPA 15 committee to see how this number was determined? You may want to contact the insurance carrier engineering department providing coverage for guidance to see what they suggest. Given the $$ at risk I am sure they will provide feedback.

 

[cdafd]

It was in the 69 edition,

Guess it has not been challenged
Maybe some testing done a long time ago??!


2) Automatic water spray systems for exposure protection should be designed to operate before the formation of carbon de- posits on the surfaces to be protected and before the possible failure of any containers of flammable liquids or gases because of the tem- perature rise. The system and water supplies should, therefore, be designed to discharge effective water spray from all nozzles within 30 seconds following operation of the detection system.

 

[cdafd]

there is this provision in 15


1.5 Equivalency.

Nothing in this standard is intended to prevent the use of systems, methods, or devices of equivalent or superior quality, strength, fire resistance, effectiveness, durability, and safety over those prescribed by this standard. Technical documentation shall be submitted to the authority having jurisdiction to demonstrate equivalency. The system, method, or device shall be approved for the intended purpose by the authority having jurisdiction.

 

[cdafd]

I am not knowledgeable with 15, but:::


Which edition of 15 are you looking at/ designing to??


from 2017:::

Should

A.7.1.6

Prompt operation of the water spray system is needed to meet the design objectives. In most installations, the delivery of effective water spray from all open nozzles should take place within 30 seconds after detection. This can be accomplished by the remote starting of fire pumps. The use of devices such as timers would delay system actuation and negatively affect the system’s intended performance.



7.1.6 *

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.

 

[MikeBP]

Yeah I have identified the 1969 version with that text which gives a intention behind the number but not the scientific reason for «30». At least it gives some sort of an answer. But I guess it has not been challenged lately.

Thanks for 1.5 (equivalency). I actually did not see that!

Contacting NFPA is a good tip. I will check out if our company is an NFPA member on monday!

 

[cdafd]

Which year edition do you have to design to???

Did you see the wording from 2017 edition

 

[MikeBP]

I am using the 2017 version. Yeah I saw it, but I did not know about the part about equivalency you showed me. Thanks