Maintaining readiness in fire hydrants

This invention relates to firefighting, and particularly to the use of potassium formate as a freeze point depressant in fire hydrants.

In northern climates, a difficult problem for firefighters has been the tendency of the water in fire hydrants to freeze. Frozen water either in the hydrant itself or in the working parts of the valves which operate it may completely prevent use of the hydrant, frustrating any timely efforts to thaw the hydrant or otherwise release the water upstream from the hydrant, thereby risking loss of life and costly destruction of property.

In recent years, a common approach to this problem has been to add one or more glycols to the water in the fire hydrant, and sometimes in the pipe segments near the hydrant valves as well. This has been successful to some degree, but glycols have a tendency to degrade, and some of them are toxic. In addition, glycols can be metabolized by microorganisms under certain conditions, creating foul smells and resulting in decreased effectiveness as a freeze point depressant.

In addition, hydrants are periodically checked for performance, necessitating a release of the contained fluid to the environment. Glycols have an additional disadvantage in that there may be regulatory and liability consequences to their release to the environment. It is highly undesirable for ethylene glycol to find its way into drinking water. Disposal of water containing glycols can be particularly difficult where hundreds of hydrants may be routinely emptied and refilled in a community.

Potassium formate has been suggested for use in solution as a heat transfer medium, as in cooling systems. See Example 2 of David F. Smith's U.S. Pat. No. 2,233,185, and Kardos et al U.S. Pat. No. 5,104,562, which discusses the freeze point of a saturated solution of potassium formate. See also Minks et al U.S. Pat. No. 6,059,996. Gavlin et al, in U.S. Pat. No. 5,853,458, propose the use of potassium formate as a solvent ingredient together with glycols.

Potassium formate was also suggested, in U.S. Pat. No. 5,993,875, to be useful for lowering the freeze point of brines used for preserving fish.

We are not aware, however, of the use of potassium formate in a fire hydrant maintenance system.

FIG. 1 is a sectional view of a common type of fire hydrant, showing how the invention is used in it.

Referring now to FIG. 1, the hydrant comprises an inlet 1 for a water source under pressure, a valve 2 manually operated through stem 3 having a hexagonal terminus 4 , and a water outlet 5 for connection to a hose. Water is present in the hydrant in two places—in the hydrant chamber 6 and entrance elbow 7 . Elbow 7 is normally beneath the surface of the earth or pavement, and may therefore be less susceptible to freezing temperatures than the exposed parts, but nevertheless can reach quite low temperatures. The water is quiescent and stationary in both the chamber 6 and the elbow 7 , and highly vulnerable to freezing particularly in the chamber 6 and in and around valve 2 .

The present invention comprises including in the water in the chamber 6 and/or the elbow 7 an amount of potassium formate effective to reduce the freeze point of the water. Effectiveness will vary with the opinion of the user, the climate or average winter temperature, the altitude, the thickness of pavement over the elbow, and other circumstances. Generally, however, a concentration of at least 10% potassium formate by weight is desirable to reduce the freezing point to a practical level where the temperature is occasionally low enough that freezing can occur. In colder climates, where surface temperatures may be as low as −30° F. for hours, at least 35% potassium formate should be used. As an economic matter, since the labor or effort to mix the potassium formate in the water will be expended more or less regardless of the amount of potassium formate added, there is little point in using a minimal amount. Therefore we prefer to use at least 15% in milder climates and at least 35 in the areas likely to have temperatures in the range of +10° F. to −30° F. in the winter.

The amount of potassium formate in a saturated solution is a function of the solution temperature. While adding more potassium formate to the water than is necessary to make a saturated solution at room temperature may be wasteful, there is no practical reason not to do so; therefore we may use solutions from 10% to saturation, but prefer to use from 10% to 20% for moderate climates and 20% to 45% in colder ones as described above.

Table 1 shows the freeze points of various concentrations, by weight, of potassium formate in aqueous solution:

Unlike the glycols, potassium formate is considered safe, and, under most regulatory regimes, may be released to the environment. In concentrations over about 7%, potassium formate is bacteriostatic. See Siv K. Howard, “Formate Brines for Drilling and Completion,” Society of Petroleum Engineers publication 30498, 1995, 483, 486. By contrast, glycols are actually metabolized by microorganisms in warm weather, creating significant stenches.

Our invention includes a regimen for the maintenance of a fire hydrant comprising, prior to cold weather (that is, weather likely to result in frozen hydrants), adding to the hydrant water chamber and/or the elbow upstream of the hydrant valve, a solution of potassium formate of a concentration effective to inhibit freezing, and, after cold weather, removing the solution; this procedure is repeated as cold weather returns. After use in firefighting, new additions should be made to the hydrant. In addition, the regimen includes periodic flushing and replenishing the potassium formate solution. Preferably, the potassium formate solution is flushed and replenished yearly, but flushing and replenishing may satisfactorily be performed every two years. The solution should be sufficient in strength to reduce the freezing temperature at least 10 degrees F., preferably 20 degrees F.