Many areas of the country use a variety of liquid salts to treat roadways during periods of snow, sleet and freezing rain. They are great for roads, but rough on fire trucks.
Salt, when mixed with water, becomes a brine solution. This solution reduces the freezing temperature of water. When using liquid salt or salt that is pre-wetted, the freezing points of water are reduced faster than when solid product is put on the roads.
Many of these products also are used to reduce the amount of damage done to road surfaces and include:
- Sodium Chloride
- Calcium Chloride
- Magnesium Chloride
- Potassium Acetate
- Calcium Magnesium Acetate
Sodium chloride, calcium chloride, and magnesium chloride are all highly corrosive to fire apparatus. These hydroscopic chlorides are more corrosive because deposits remain moist and allow corrosion to occur for a much longer period.
Menace to fire trucks
Many road-treatment chemicals contain corrosion inhibitors to reduce the corrosion rate on a metal or alloy; however, corrosion inhibitors are metal specific and salt specific. No one corrosion inhibitor will prevent corrosion to all metals.
Although these salts have been embraced by local governments, environmental groups and the snow-removal community, fleet managers are becoming increasingly distraught over their use.
Why? Because their use has accelerated the rust and corrosion of fire apparatus and other emergency response vehicles causing increased apparatus maintenance costs and a decrease in the fire apparatus lifecycle.
Fire apparatus manufacturers have been successful in increasing the life span of their vehicles. However, the impact of these next-generation salts is creating a new set of problems.
These pre-emergent salts are able to stick to vehicles longer and are more active at lower temperatures. As a result, the apparatus is experiencing severe body rust, part failures and something new — wiring-harness issues — all because of corrosion.
Staying on top of corrosion issues can extend the life of fire apparatus and other vehicles and reduce repair costs and vehicle downtime.
Types of corrosion
There are six forms of corrosion that are commonly associated with all motor vehicles: uniform, crevice, poultice, pitting, galvanic and filiform. Some may be new to the reader — or may give a name to a problem that’s been known all along.
Uniform corrosion spreads out at the same rate over a metal surface. This form of corrosion is particularly damaging to fire apparatus because it affects the underside of the vehicles including electrical harnesses.
Crevice corrosion is a localized form of corrosion that affects metals that are attached or adjacent to one another. One of the metals may be shielded from the full effect of the environment.
Poultice occurs when road salts and debris accumulate on vehicle ledges. This accumulated materials is kept moist by the environment and washing the vehicles. Damage to vehicles occurs during the drying process.
Pitting occurs to metals that are not fully resistant to corrosion. Cellular-level action produces cavities within the surface of the metal.
Galvanic corrosion is an accelerated form of corrosion that occurs when two dissimilar metals come in contact with one another. One of the more prevalent problems that occur in fire apparatus is when aluminum and steel come in contact with one another.
Filiform corrosion occurs under the surface of an organic coating. This type of corrosion is seen with aluminum and magnesium alloy metals. This will occur when voids are created in the organic coating.
Undetected attack
Corrosive road salts attack a variety of metal components that include frame rails, cross-members, suspension components, air tanks, fuel tanks, battery boxes, brackets, brake shoes, electrical systems, air conditioning condensers, radiators, metal coolant tubing and steel wheels.
Calcium and magnesium chlorides get quite viscous as water evaporates, collecting sand and dirt and form compacted deposits in recessed areas. These difficult-to-remove deposits are the source of major chloride corrosion.
Further complicating the situation, if the road salts are not removed from the vehicle, magnesium chloride and calcium chloride will pull moisture out of the atmosphere, rewet and continue their corrosive action.
One of the problems associated with corrosion is that it can go undetected for lengthy periods of time before a major problem begins to surface. If corrosion can be identified early and corrective measures are taken, the damaging effects of corrosion can be reduced.
Here are nine steps to preventing corrosion.
- When fire apparatus has been worked on, reapply protective coatings to areas that may have been damaged by the process. Before treating vehicles, make sure that the underside and wheel wells are not packed with mud, salt or snow.
- Inspect electrical systems on a regular basis as corrosive chemicals can damage electrical wiring and harnesses that are exposed, such as connections or areas that have been spliced.
- Clean electrical connectors regularly with plain water and re-grease with dielectric grease.
- Thoroughly wash the undercarriage. High-pressure washer equipment can push the chemicals farther into cracks and crevices; there is some debate regarding high-pressure vs. low-pressure washing. Follow manufacturer recommendations.
- Inspect the undercarriage frequently to identify corrosion early.
- Hose the radiator with plain water.
- Keep mud flaps in good repair to minimize the salt spray.
- Avoid splicing wires.
- In spring, thoroughly wash the vehicle’s undercarriage and apply a rustproofing compound.
Spring is also a good time to conduct a thorough visual inspection of the vehicle, including those hard-to-reach spaces and crevices, to get the upper hand on any corrosion or damage that may have occurred during winter operations.
To ensure that your department gets the most service life from a piece of fire apparatus, assume that the effects of rust and corrosion start from the day you put the vehicle in service regardless of the season. Road de-icing chemicals stay on roadways year-round and are constantly being collected by fire apparatus going up and down the road, especially during rainy weather.
In the words of that “olde” firefighter, Benjamin Franklin writing as Poor Richard, “An ounce of prevention is worth a pound of cure.”
