Antifreeze in Wet Fire Sprinkler Systems
By George Rudolph
When it comes to antifreeze for fire sprinkler systems, the past twelve months have been a period of anticipation and uncertainty for engineers, manufacturers and contractors alike. Following a temporary ban on the use of antifreeze, coupled with proposed legislation mandating fire sprinklers in new residential construction, there was plenty to talk about in the industry. As I write this article, there have been two fatal fires in the last 24 hours in my community, resulting in the loss of three lives. While the results of these tragic incidents cannot be reversed, they reinforce the critical role which fire sprinkler systems play in protecting lives.
Following a well-publicized fire incident involving a fire sprinkler system with a very high concentration of antifreeze, the NFPA began independent testing to determine the risk of combustion posed by antifreeze in residential fire sprinkler systems. The testing centered on the two most common types of antifreeze used in wet systems, glycerine and propylene glycol. Other solutions are less frequently used and are now prohibited, due to toxicity concerns. While antifreeze has been used in fire sprinkler systems for decades, the testing established safe levels which, under fire conditions, do not contribute to an increase in heat or fire intensity, but rather perform similar to water.
In March, the NFPA issued a new set of TIAs (Tentative Interim Amendments) which establish new approaches to the use of antifreeze in both new and existing residential occupancies, as well as in non-residential occupancies. These TIAs also introduce new requirements for the testing, maintaining and tagging of such systems. I have received hundreds of calls and emails regarding the use of antifreeze, and it is apparent that there is a broad range of understanding of the issue amongst fellow industry colleagues. So let’s take a look at the specifics and identify the changes which will affect design and maintenance going forward.
Maximum allowable concentrations
Effective March 21, 2011, NFPA limits the use of antifreeze in wet fire sprinkler systems to either glycerine or glycol. Ethylene glycol and other antifreeze fluids that are toxic are no longer permitted. In the past, field mixing was permitted to desirable freeze protection levels; however, the new standards limit solutions to factory pre-mixes only (no concentrates allowed), with a maximum concentration by volume of 38% propylene glycol or 48% glycerine in new systems. (It should be noted that existing systems are allowed a concentration of up to 40% propylene glycol or 50% glycerine). For the vast majority of the United States, these concentrations provide sufficient freeze protection levels. However, contractors in regions subjected to extended periods of sub-zero temperatures will need to consider additional freeze protection methods in conjunction with antifreeze.
Limiting the use of antifreeze to factory pre-mix solutions will eliminate the inconsistencies found with field mixing techniques. Glycerine is a particularly difficult solution to mix in the field, as it begins to thicken in concentrate when temperatures drop to just 62 degrees Fahrenheit. Field mixing methods employed in the past ranged from manual agitation to mixing with a wooden paddle to simply pouring concentrate into a system and adding water. Usually, the end result was a piping system with varying degrees of antifreeze concentration. There is no viable field mixing method that provides a consistent and homogenous formulation like that of a factory pre-mixed solution.
Testing and maintenance: changes and challenges
With new guidelines having been established, the next few months will see an enormous increase in system testing and fluid replacement. Where antifreeze concentrations exceed allowable limits by volume, these systems will need to be drained and a new lower concentration of antifreeze introduced into the system. Adding concentrate to an existing system is no longer an option. As a result, accuracy in testing methods becomes increasingly critical. There are many testing instruments available for use; however, testing accuracy varies greatly depending upon both the type of device and the antifreeze used.
Propylene glycol concentration can be tested with a simple analog refractometer, which will display a freeze temperature on a graph that is visible through a viewfinder. Based on the freeze point, interpolation from a chart (usually provided on the manufacturer’s product label) will yield the concentration level. Propylene glycol concentrations of 38% generally offer freeze protection levels of 0 to -5 degrees Fahrenheit.
Glycerine is more of a testing challenge, in that traditional analog refractometers are not suitable testing instruments. The older and more “scientific” method of testing utilizes a lab-grade hydrometer. The hydrometer is suspended in a graduated cylinder containing a sample of the antifreeze solution. A specific gravity or specific density reading is obtained at a given temperature. The reading is then converted to freeze point on a chart, based upon the given temperature and density. A solution of 48% glycerine generally provides a freeze point of about -15 degrees Fahrenheit.
A much more accurate method (and more expensive) is that of a digital refractometer. These devices are temperature-compensating and provide freeze point and concentration by volume in a matter of seconds. Unlike hydrometers, there is no conversion chart necessary and accuracy is plus or minus one tenth of one percent. Digital refractometers can be factory-calibrated to test both propylene glycol and glycerine solutions, making them the best choice for system testing.
Testing of new systems must now take place using samples drawn from both a high and a low point in the system (multiple test points need to be designed into systems). Both samples should yield similar test results. Additionally, a sample of the antifreeze should be taken prior to introduction into the system, and that sample reading should also closely approximate the two samples drawn from the system.
Consideration should be given to the fact that fluid trapped or not drained from drops in existing systems could slightly alter refractometer readings. In any case, attempts should be made to test from multiple points, and NFPA guidelines should always be followed with regard to testing procedure and frequency.
Finally, all new and existing systems are now required to have a placard, or tag, affixed to the riser indicating the type of antifreeze, system volume, antifreeze concentration by volume, the date and the name and license number of the contractor performing the work. Leading industry manufacturers of fire sprinkler antifreeze products provide these tags at no charge.
Where do we go from here?
Undoubtedly, one common question which will arise with all of the “drain and replace” activity which has begun is “What do I do with the old antifreeze?” The simple answer is to follow local and state jurisdictional requirements regarding the disposal of antifreeze solutions. Propylene glycol and glycerine are both non-toxic, and usually may be disposed of in sanitary sewer systems. Glycols should never be disposed of in a storm sewer or on the ground, where the possibility of migration into the watershed exists. As glycol breaks down, it produces an oxygen-depleting byproduct which can harm aquatic life.
Just as fire sprinklers will continue to play an increasingly critical role in the preservation of life and property, antifreeze solutions in these systems will continue to ensure system operation in environments where freezing temperatures could lead to system failure. For additional information or clarification on antifreeze use in wet fire sprinkler systems, I encourage you to contact me or your local jurisdiction having authority.
George Rudolph is the national sales manager for Noble Company.