In large areas of the country, the road salt season starts as early as October and can last into April. If you respond in an area where road salt is a fact of life, it’s time to start thinking about how to protect your fire apparatus and ambulances from the corrosive nature of the salts used to keep roads and highways free of snow and ice.
Spreading salt on slick roads lowers the freezing point of snow and ice. When cities add salt to the roadway, the freezing point drops from 32 degrees F to 20 degrees F or lower. Salt also helps drivers gain more traction during severe weather situations.
Now, those are the positive aspects of salt on roads. The downside is that, when salt gets on your fire apparatus and stays there, it can promote rust in all sorts of places on your apparatus.
Salt buildup can occur in just about any area of your fire apparatus or ambulance, but it is especially common on areas affected by road spray. This includes fenders, wheel wells, fuel tanks, rocker panels and more.
Here’s another twist. Salt, when mixed with water, becomes a brine solution. This solution also reduces the freezing temperature of water. In many areas of the country – particularly those “salt-belt states” – local and state highway departments are pre-treating road surfaces with a pre-mixed brine solution that helps prevent ice from accumulating on the roadway in the first place. These brine solutions also reduce the freezing point of water faster than their solid-salt cousins.
Reducing salt’s impact on your apparatus
Here are nine steps to preventing corrosion to your apparatus:
- When maintaining fire apparatus, 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 exposed electrical wiring and harnesses, 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.
Worst states for road salt
The worst states for rust come from an area known as the “Salt Belt.” State government trucks dump large amounts of the chemical compound onto roads in certain areas of the country, causing cars to experience more destruction and rapid rusting compared to other parts of the region. States in the “Salt Belt” include:
- Alaska
- Connecticut
- Delaware
- Illinois
- Indiana
- Iowa
- Maine
- Maryland
- Massachusetts
- Michigan
- Minnesota
- Missouri
- New Hampshire
- New Jersey
- New York
- Ohio
- Pennsylvania
- Rhode Island West Virginia
- Vermont
- Virginia
- Wisconsin
- Washington D.C.
Menace to fire trucks
Highway departments must also concern themselves with the damage that salts inflict on the road surfaces themselves. They do so by using products like these to reduce the amount of damage done to road surfaces:
- 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 hygroscopic chlorides are more corrosive because deposits remain moist and allow corrosion to occur for a much longer period.
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, and 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 these pre-emergent salts can stick to vehicles longer and are more active at lower temperatures. As a result, the apparatus is experiencing severe body rust, part failures and wiring-harness issues, all because of corrosion.
Apparatus corrosion and damage
There are six forms of corrosion that are commonly associated with motor vehicles that may impact your apparatus. Some of these may be new to you or may give a name to a known problem.
- Uniform corrosion spreads out at the same rate over a metal surface and is particularly damaging to fire apparatus because it affects the underside of the vehicles, including electrical wiring harnesses.
- Crevice corrosion 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 material is kept moist by the environment and washing the vehicles. Damage to vehicles occurs during the drying process.
- Pitting happens 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. Most common problem for fire apparatus? When aluminum and steel encounter one another.
- Filiform corrosion occurs under the surface of an organic coating and is most commonly seen with aluminum and magnesium alloy metals. The corrosion occurs when voids are created in the organic coating.
Undetected apparatus 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 (those hygroscopic chlorides) get quite viscous as water evaporates, collecting sand and dirt and forming compacted deposits in recessed areas. These difficult-to-remove deposits are the source of major chloride corrosion.
If not removed from the vehicle, hygroscopic chlorides will pull moisture out of the atmosphere, re-wet and continue their corrosive action.
This article was originally published in 2018 and has been updated with a video.
