Max firewater demand scenario 2

[CTEmanager]

I am new to fire area. I learnt that the capacity of firewater supply system (or station) for a petrochemical plant should be equal to the maximum firewater demand scenario only. There is no need to cover 2 or 3 scenarios at the same time.

Can anyone tell me relevant NFPA chapter for the above sentences.

 

[stookeyfpe]

Neither NFPA or API have no standards that establish the required fire flow for a petrochemical plant.

 

[fel3]

The normal standard of practice is to design water systems (in your case apparently a dedicated firewater supply system) to handle ONE maximum fire demand scenario. However, the requirements for your system ultimately must come from the fire department with local jurisdiction. They will likely base their requirements on NFPA, ISO, AWWA, building codes, other standards, fire studies, etc., but local conditions can supersede these standards. I'm at home today, but as I recall, AWWA M32 (Computer Modeling of Water Distribution Systems) specifically mentions the single fire demand scenario as being standard practice. I've read this other places as well, but off the top of my head I can't remember where. As far as I know, this is not carved in stone is a code or standard, but is simply a reasonable and long-used standard of practice.

Years ago, a gas and diesel tank farm I consulted for was annexed by the local city. The local county had required next to nothing for fire protection (a single 750 gpm well pump and a loop of 4" pipe with wharf head hydrants), but the City had other ideas. I worked closely with the city's fire department to establish the design criteria for the new fire protection system. The fire engineer I worked with showed me some forensic studies for fires at other tank farms. As I recall, these studies indicated that, in the absence of a foam system, a fire flow on the order of 10,000 gpm to 15,000 gpm was required to suppress the worst of the fires. With a foam system, about half that was required. Unfortunately, the nearest city main was almost two miles away. There was a small semi-rural water company about 3/4 mile away to the edge, but that system was barely able to supply it's maximum fire of 1500 gpm. In the end, we agreed on two 2500-gpm diesel-driven well pumps feeding loops of 12-inch pipes, and a foam injection system. I had modeled the water company's system and determined that the well and piping upgrades that would have been required to enable that system to serve the tank farm were better and cheaper placed at the tank farm.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[chicopee]

That statement of yours "... I learnt that the capacity of firewater supply system (or station) for a petrochemical plant should be equal to the maximum firewater demand scenario only..." is analogous to determine the capacity of a dike for bulk storage tanks whereby the volume of the dike whould be based on the volume of the largest storage tank within the containment.
While stookeyfpe's statement is true, the NFPA has codes for specific installations and equipment used by petrochemical plants. Before you start digging for these codes, you should read the Fire Protection Handbook in which specific subjects are covered. For example there are sections such as Chemical Processing Equipment, Storage and Handling of Chemicals, Automated Process Equipment, controls of electrostatic ignitions, Flammable and Combustible liquids and the list is endless for your petrochemical plant. You also have OSHA regulations such as Process Safety Management. You can also contact your fire insurance carrier since insurance companies have guidelines for the quantity (in gpm)of water, duration (in minutes or hours) of the water supply, requirement on the number of fire hydrants, installation of chemical extinguishing system, number of portable fire extinguishers.

 

[LCREP]

Also check out Factory Mutual Data sheets they are free. They will give you info from an insurance point of view. They also give you a good overview of the hazards and controls of an operation. Did i mention they are free!

Link

They have a lot of good information on this topic.


7-46 Chemical Processing Reactors and Reactions


7-47 Physical Operations in Chemical Processing Plants


7-14 Fire Protection for Chemical Plants

3-26 Fire Protection Water Demand for Nonstorage Sprinklered Properties


7-42 Evaluating Vapor Cloud Explosions Using A Flame Acceleration Method

 

[CTEmanager]

Thank you to all answers.

“To minimum firewater supply capacity, the governing fire water rate for the Project has been determined by splitting the area in subdivisions for which the maximum extent of any single fire has been established. Each subdivision is separated from all others by a minimum of 15m clear space.”

Can anyone provide me reference or concept for “15m clear space”. How to determine a typical clear space if 15m is not suitable.