With ever increasing pressures to remove fluorinated foams from the marketplace, one segment in particular seems to have been overlooked especially with governmental regulators who oftentimes have legislative desires that exceed the technology that is currently available.
That market segment is the use of firefighting foams in conventional sprinkler and spray systems to suppress class B flammable liquid fires. With the development of film forming firefighting foams in the 1960’s came the ability to use these foams in non-air aspirating sprinkler and spray heads where, previously, only air aspirating discharge devices could be employed. Typical applications where conventional sprinkler heads and spray heads are utilized include aircraft hangars, bulk fuel loading racks, manufacturing process areas, fuel storage areas, backup/emergency power systems and warehouse facilities. Both open (deluge) and closed head systems may be used to protect these high-risk applications.
The actual design requirements for a sprinkler system that employs firefighting foam can be found in International Standards such as NFPA 11:Standard for Low-, Medium-, and High-Expansion Foam, NFPA 16: Standard for the Installation of Foam-Water Sprinkler and Foam-Water Spray Systems, NFPA 30: Flammable and Combustible Liquids Code, and NFPA 409: Standard on Aircraft Hangars. All of these Standards require the use of Approved or Listed foams that have been specifically tested for use in sprinkler or spray systems. Foam performance standards include UL-162 Standard for Foam Equipment and Liquid Concentrates, ULC-S564 Standard for Category 1 and 2 Foam Liquid Concentrates, and FM-5130 Approval Standard for Foam Extinguishing Systems have very stringent testing protocols to determine the effectiveness of the firefighting foam when deployed through standard sprinklers (non-air aspirating sprinkler heads) or non-aspirating spray nozzles. Many fluorinated firefighting foams cannot pass these sprinkler performance standards.
Foam-water system conversion
Fortunately, there are a limited number of fluorine free foams that can pass these tests and are certified to UL, ULC, and/or FM standard sprinkler Listings and Approvals. This fact allows end-users who have non-air-aspirating sprinkler and spray systems already installed to look at converting those existing systems over from fluorinated foams to fluorine free foams and still be assured that they will perform at the same level of performance as they were originally designed for.
Converting an existing fluorinated foam system over to a fluorine free foam system can, in some instances, be as simple as changing out the fluorinated foam product for the fluorine free foam product and, perhaps, changing an orifice plate on a proportioner (ratio controller).
Things in the real world however are rarely, if ever, simple. Most foam changeouts will require the same amount of design work to ensure adequate protection is provided. It is recommended to engage a fire protection engineer, special hazard suppression company or sprinkler contractor prior to designing a retrofit system.
In many cases, the sprinkler heads will not need to be changed. Ultimately, the Authority Having Jurisdiction (AHJ – insurance underwriter or the fire marshal or the corporate safety director etc.) may dictate the required protection. If the sprinkler heads need to be changed out it is important to use discharge devices that are listed/approved with Fluorine Free Foam.
Foam hardware options
The proportioning system design and hardware selection is one of the most critical aspects of the foam system design ensuring that the correct mix ratio of foam concentrate to water is accomplished. Foam systems may be designed to proportion from 1% to 6% depending on the foam concentrate selected. The area that may require the most in terms of engineering is the proportioning system that is used to get the correct mix ratio of foam concentrate to water. Most systems are set up for a 3% mix ratio but 6% and even 1% systems are also used. There are three commonly used proportioning systems in use today. These are Balanced Pressure Bladder Tank Systems, Balanced Pressure Pumped System and Direct Injection Foam Pump Systems.
Probably the most installed and simplest proportioning system is the Balanced Pressure Bladder Tank System. This system does not require any auxiliary power to pressurize the foam concentrate but, rather, relies on the motive force of the system water to provide foam concentrate under pressure to the orifice plate of the ratio controller. In converting this type of proportioning system, the percentage of the concentrate (i.e. 1%, 3% or 6%) must be the same between the fluorinated foam and the Fluorine Free Foam or else the size of the bladder tank may have to be adjusted. It is important to look carefully at the hydraulics of the concentrate piping as some foam concentrates may not possess the same flow characteristics. In particular, the length of run from the bladder tank to the ratio controller can be a critical element. Often, the orifice plate in the ratio controller must be changed to accommodate the different foam concentrate.
Alternatively, the entire ratio controller might have to be changed out at the discretion of the AHJ. Finally, an alternative, and perhaps the best option is to change out the entire bladder inside the bladder tank so as to minimize any fluorinated foam carryover and to ensure that the old bladder is not worn or damaged.
Another common method of proportioning is the Balanced Pressure Pump System. This type of system uses a positive displacement pump to provide foam concentrate under pressure to the orifice plate of the ratio controller at the same pressure as the system’s flowing water pressure. This balancing of pressure is accomplished by means of a pressure balancing valve (diaphragm valve or spool valve) along with a concentrate return line to the main foam concentrate storage tank. Any foam concentrate that is not required by the system flow demand is returned to the concentrate storage tank. Unlike in Balanced Pressure Bladder Tank Systems which utilizes a pressure vessel to hold the concentrate inside the bladder, a Balanced Pressure Pump System can utilize an atmospheric foam concentrate storage tank. As with bladder tank systems, the concentrate piping hydraulics going from the pump to the orifice plate of the ratio controller must be evaluated for pressure loss. Also, the fluid paths of the balancing valve(s) will need to be evaluated to ensure that they are sized properly to allow balancing. Additionally, the suction side piping feeding the pump must be looked at and, if necessary, upsized so that the pump is not starved by potentially more viscous concentrate.
Diesel Driven Foam Pump Skid
And finally, the pump’s rotational speed must not be so high that the fluid cavitates inside the pump cavities. In some instances, it may be necessary to change out the positive displacement pump to accommodate the viscosity of the Fluorine Free Foam.
In recent years, Direct Injection Foam Pump Systems have become increasingly popular. These systems utilize a positive displacement pump that is driven by the motive force of the water flowing to the sprinkler heads. As the demand to the sprinkler heads increases (i.e. more heads open in a closed head system or more zones are activated in a deluge system), the amount of foam concentrate injected into the system increases. As with Balanced Pressure Pump Systems, fluid hydraulics and concentrate viscosity must be taken into consideration when switching over to a Fluorine Free Foam.
An easy decision
At a time where most of the discussion on firefighting foam transition is centered on foam stock changeouts or emergency response tactics to large tank storage fires, fixed foam-water systems have gone unnoticed. Yet, the same regulatory pressures abound; irrespective of if the foam is a stored in a container, is a piece of mobile equipment or part of a fixed system utilizing non-air-aspirating sprinkler or spray nozzles. End-user customers should not fail to notice the importance of fixed foam systems, but rather they would be wise and strategic in their approach, to capture “wins” by addressing these system installations as part of their overall risk management planning.
As to system conversion, the end-use customer would be best suited to consult their inhouse fire protection resource(s), local AHJ or insurance underwriter as a first start. Ultimately the system conversion would need to be facilitated by a special hazard suppression company or sprinkler contractor. Compliance with International Standards such as NFPA along with selection of the Fluorine Free foam concentrate and system hardware components that are tested and certified to stringent performance standards such as UL, ULC or FM is critical to assure the system will perform as designed.
For more information, go to www.solbergfoam.com