Fire fighting strategy and tactics textbooks as well as conventional fire fighting wisdom often advise the public fire service not to use private (yard) fire hydrants. Insurance companies have also discouraged or attempted to limit their use by public fire departments.
The reasons for this are:
Using water from the yard hydrant robs water from the sprinkler system which can result in loss of control of the fire by the sprinklers.
- Yard hydrant maintenance is unreliable thereby putting firefighters at risk because of an unreliable water supply.
These reasons are valid and there have been negative consequences for failure to adhere to them. Ideally, sprinklers and hydrants would be supplied by independent water supply systems to provide a level of redundancy. This is common practice in some countries.??
A reason that is not often stated but has caused serious problems is that yard hydrants may have pressures of 150 psi or even more. The public fire service is often unaccustomed to this kind of intake pressure. Initially "normal" intake pressures may suddenly surge as fire pumps come on line. Sometimes the fire department pumper will act as a gate valve to choke down pressure rather to than boost it. Pumper operations with extremely high intake pressures are beyond the scope of this article. The best way to prepare for this is to practice at sites with the high pressures under the command of experienced pump operators and safety officers who have carefully thought through and researched such operations.?????????????
It has often been said that the answer to all fire protection questions is "it depends," and that is certainly true in the case of the use of yard hydrants by public fire departments. In general, where reliable public hydrants are available, they should be used instead of yard hydrants.
The concern over yard hydrants goes back over one hundred years when yard water supplies may have been supplied by a manually started steam fire pump. The facility was likely in the center of town and public fire hydrants supplied from gridded mains were close by. Sprinkler system rules at the time did not quantify the simultaneous use of hydrants. Yard hydrant use was anticipated to supply hose streams operated by the in-house fire brigade.
While the concerns are still valid today, the use of yard hydrants by public fire departments may be necessary in today's industrial facility. Sprinkler standards today require that a certain flow rate be available for simultaneous fire hose and sprinkler system operation. Industrial facilities are more often located on the outskirts of towns where public fire hydrants are not readily available. Lack of maintenance should no longer be an excuse. If reliable water supplies are provided and the guidelines in NFPA 25, Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems are followed, there is no reason a private supply cannot have acceptable reliability. And there is no reason why the public fire department cannot insist that NFPA 25 be followed.
Consider the following example:
An approximately 1 million square foot distribution center is located in a suburb of a major city. There is a reliable county water supply that feeds the facility's underground fire loop. County water pressure is boosted by a private fire pump. The facility also has a private water tank which also supplies the underground loop through a second private fire pump. There is a public hydrant at the entrance to the facility; however it would be at least a 2,500 foot hose lay to reach the back of the facility. Private hydrants are distributed at approximately 250 foot intervals along the private main that encircles the facility.
This same scenario can easily "scale up" to circumstances where the nearest public hydrant would require a mile or more of hose to reach the most distant parts of the facility.
Many other facilities are so far out of town that the available public water supply may be of little more value than filling up the private water supply tanks. Still others are so large that their private water supplies start to resemble the "water works" of a small town and may be more reliable than the nearby city.
Through proper preplanning, the public fire department can determine if it would be better off using private hydrants instead of public hydrants. We will take a detailed look at the original concerns.
Robbing the sprinkler system
Sprinklers are the most effective means of controlling fires in industrial buildings. If the public fire department uses excessive water for hose streams, they may take water that is being used effectively by the sprinklers and fire control may be lost. If a sprinkler system design anticipates 500 gpm for fire hose use and a public fire department sets up two 1,000 gpm deluge guns, the effectiveness of the sprinklers will likely be reduced, probably to the point of loss of fire control.
To prevent public fire departments from using too much water, most yard hydrants have only two 2?-inch outlets. If a yard hydrant is found with a 4?-inch or five-inch pumper outlet, the insurance company may have asked that it be welded shut. The idea is that by limiting the size of the hydrant outlets, the public fire department cannot use too much water and cannot rob the sprinkler system. Besides, if the sprinklers are doing their job, there should be no need for excess water.
Hose stream allowances are typically 250 gpm where Early Suppression Fast Response (ESFR) sprinklers are used or where ordinary hazards as defined by NFPA 13 Installation of Automatic Sprinkler Systems are present. This is increased to 500 gpm for storage protected by non-ESFR sprinklers or for extra hazard manufacturing operations. Highly Protected Risk (HPR) insurance companies or third party loss prevention consultants may specify a greater hose stream allowance. The key is to find out through preplanning what hose stream allowance has been anticipated and to be sure that you don't exceed that amount from a hydrant(s) water supply (private or public) that also serves the sprinkler system.
If a hazard has increased since the sprinkler system was installed, an agreement may be reached where the hose stream allowance is reduced, thereby saving more water for the sprinklers. The public fire service is then expected to bring in the extra hose stream water from another source. This should be carefully coordinated with the public fire service to be sure that they can do this. It is a mistake to simply say, "well, there is a good public main a block away and the fire department can just get the hose stream water from there." That may be an entirely workable solution, but the public fire department needs to agree to it and make it part of their pre-emergency plan.
This is something the fire service has more control over than they may think. First of all, municipal water supply reliability is far from assured. In my experience, I have found just as many water supply problems (shut valves, damaged hydrants, etc.) on public supplies as on private supplies. As we have tried to emphasize throughout this column, the fire service is empowered to ensure reliability through enforcement of existing ordinances like NFPA 25 or passing such ordinances if they are not in place.
The public fire service thinks nothing of using a standpipe in a high rise building and a private hydrant can be thought of as an outlet on a horizontal standpipe. In most cases, there is a fire department connection that can be used to supplement the system that should be used. In my experience, where there is no fire department connection, it is because there is no credible public supply nearby; however, the private water supply usually has built in redundancy. If the private system is designed, commissioned and maintained to appropriate standards, the reliability should normally be acceptable.
A case against reliability could be made where a single water supply - such as a single electric fire pump taking suction from a single above ground tank - would not be considered reliable enough to commit firefighters to the end of a nozzle deep in a large industrial building. This is yet another circumstance where the fire service should let its concerns be known so that the water supply can be improved to an appropriate level of reliability.
The argument can also be made that the fire service does not know that the sprinklers are adequate for the hazard that is present. The counter argument is that this is knowable with adequate preplanning. It is true that the hazard could change the day after the pre-plan but the hazards are usually there long before the fire and are there to be discovered.
If the public fire department determines that the yard hydrants are not reliable enough to use, they need specific plans on how to move water potentially several thousand feet from the nearest reliable supply. The apparatus and staffing doing this should be part of initial response. This could become an automatic second or third alarm response to ensure that there are enough resources to provide the needed hose stream water.?????
From a reliability and fire control perspective, it is clearly better to supply fire hose streams from public hydrants that will not take water away from the sprinkler system. Further, yard hydrants can deliver extremely high pressures and fire department pump operators may lack the needed experience. However, there are several circumstances in today's environment where yard hydrants may be a viable option. This article helps the public fire department, loss prevention engineer and facility management understand when it may be necessary to use yard hydrants and how that can be done safely and reliably and without compromising the effectiveness of the sprinkler system.
We encourage comments back to the editor. We will collect and address the comments in a later article.??????????????????????????????????????????
Feel free to contact this author at John.Frank@xlgroup.com or at (404) 431-2673.????????????????????
John Frank, P.E., CFPS is with XL GAPS, a leading loss prevention services provider and a member of the XL Capital group.?"XL Insurance" is the global brand used by member insurers of the XL Capital Ltd (NYSE: XL) group of companies. More information about XL Insurance and its products is available at www.xlinsurance.com.