Dealing with foam system proportioning issues can be frustrating and time consuming.  This guide is designed to help explain what the requirements are and what you can do when your system isn’t proportioning correctly.

NFPA Requirements

The National Fire Protection Association (NFPA) requires the concentration be verified when the system is installed as part of the acceptance tests.  NFPA 11 “Standard for Low-, Medium- and High-Expansion Foam” requires a foam system to proportion at no less than the rated concentration and no more than 30 percent or plus 1 percentage point (whichever is less) above the rated concentration.  Note, the same criteria are also a requirement of NFPA 16 “Installation of Foam-Water Sprinkler and Foam-Water Spray Systems.” Table 1 provides a list of acceptable solution concentration ranges for typical foam concentrates meeting the NFPA recommendations.

Rated Concentration

Acceptable Solution Concentration

1%

1.0% - 1.3%

2%

2.0% - 2.6%

2.75%

2.75% - 3.6%

3%

3.0% - 3.9%

6%

6.0% - 7.0%

Table 1. Acceptable solution concentrations for acceptance tests per NFPA 11 and NFPA 16.

 NFPA also requires the concentration be verified annually.  NFPA 25 “Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems” requires the subsequent concentrations to be within 10% of the original acceptance test concentration but never more than 10% below the designed concentration.  If the original acceptance test results are not shared with Dyne, the solution will be tested to meet the acceptance test requirements.

Please note that NFPA 412 “Standard for Evaluating Aircraft Rescue and Fire-Fighting Foam Equipment” has its own requirements as shown in Table 2.

Rated Concentration

Acceptable Solution Concentration

1%

1.0% - 1.3% (for all nozzles)

3%

2.8% - 3.5% (for turret and ground sweep nozzles); 2.8% - 4.0% (for hand line and under truck nozzles)

6%

5.5% - 7.0% (for turret and ground sweep nozzles); 5.5% - 8.0% (for hand line and under truck nozzles)

Table 2. Acceptable solution concentrations per NFPA 412.

IMO Requirements

The International Maritime Organization (IMO) MSC.1/Circ. 1432 “Revised Guidelines for the Maintenance and Inspection of Fire Protection Systems and Appliances” requires all proportioners and other mixing devices be mixing at -10% to +30% of the nominal mixing ratio as defined by the system approval.  Table 3 lists acceptable concentration ranges for typical foam concentrates meeting IMO 1432:

 

Rated Concentration

Acceptable Solution Concentration

1%

0.9% - 1.3%

2%

1.8% - 2.6%

2.75%

2.475% - 3.6%

3%

2.7% - 3.9%

6%

5.4% - 7.0%

Table 3. Acceptable solution concentration per IMO 1432.

Note that IMO 1432 requires the solution concentration be verified at least once every five years after the initial approval.

 What do you do when your system isn’t meeting the requirements?

The following is a list of the more common reasons a system may not be proportioning correctly:

  • Incorrect solution flow - When the sample was taken, the system may have not been flowing within its rated flow range or for the time required for the system to stabilize. All proportioning systems, whether a bladder tank, pump system, or educator, are designed to proportion foam correctly but only when operated at a specific flow range. Many times, inspectors run the system at a low flow for a short time in order to generate less foam solution - which is often costly to dispose of. If this flow is below the rated flow range or if the system has not operated for a long enough time to stabilize, a system will not proportion correctly. To determine the rated flow range and suggested flow time, contact the manufacturer of the proportioning equipment or refer to the foam’s listing agency directory (e.g. UL) for the listed flow range.
  • Foam concentrate in the lab is not representative of what was used in the field – The most common way to determine the percent of foam concentration in solution is to measure the solution’s refractive index or conductivity and compare the values to those of standard solutions that are made by mixing the foam concentrate and water at known concentrations.  Note that NFPA recommends conductivity in the field due to equipment limitation but the refractive index method is allowed provided the instrument used has enough accuracy to determine solution differences.  For IMO solutions that use salt water, the conductivity method will be unreliable due to the salt’s extremely conductive properties.  Dyne utilizes the refractive index method to determine solution concentration with a laboratory grade refractometer. 

 When using either method, the foam concentrate and water used to make the standard solutions MUST be representative of the foam concentrate and water proportioned by the system. For example, a bladder tank generally proportions foam by expelling concentrate from the top of the tank. If the foam concentrate samples used to make the standard solutions are pulled from the bottom of the tank, the standard solutions might not be representative of system solution. Similarly, water taken from the shell of the bladder is not representative of the system water that is used to by the proportioner.

  • Improper concentrate and water pressures – Different systems have varying requirements for the balance between the pressures of the concentrate line and the water line into the proportioner.  Systems using a bladder tank require that these pressures are equal, while systems using a pump may have different requirements.  If the foam or water pressures are unequal, the resulting solution could have too much foam or too much water.  The manufacturer would be able to answer questions about these pressures for your specific equipment.
  • Equipment and foam compatibility issues – The foam concentrate used in the system should be listed for use with the equipment as recommended by NFPA 11. When a foam and equipment are listed together, it ensures the user that the system was tested by an independent laboratory and the system proportioned that foam correctly. There may be cases where the foam has been changed to handle a new hazard. If the new foam is more or less viscous than the previous foam, the orifice may not be sized correctly. Again, check with the equipment manufacturer to make sure the equipment is listed with the specific foam concentrate.

There can be other reasons in addition to those listed here that may cause a system to proportion incorrectly.  Training is highly recommended for any technician performing and troubleshooting proportioning tests.  To better understand your specific system, it is recommended that you contact the equipment manufacturer.  Also consider any growing environmental regulations before flowing your system.  Dyne Fire Protection Labs is also available to help you obtain the necessary resources.  Dyne can be reached at (800) 632-2304 or lab@dyneusa.com

Dyne Fire Protection Labs

2357 Ventura Drive, Suite 108
Woodbury, MN 55125
Phone: 651-917-0644
Fax: 651-917-0646
Toll Free: 800-632-2304
 

Dyne Fire Protection Labs

2357 Ventura Drive, Suite 108
Woodbury, MN 55125
Phone: 651-917-0644
Fax: 651-917-0646
Toll Free: 800-632-2304
 

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