When you notice a broken light on your fire truck, your first reaction often is, "Who did this and why didn’t anyone mention it?" As you begin to remove the lens, you notice a large amount of cracking around the screw holes. Your next thought might be, "Someone must have over tightened this lens." But as you inspect further, you find the same cracking on all of your lenses. This prompts a call to the truck manufacturer so you can complain about these “junk” lights.

The manufacturer politely assures you that the lights are not junk and they were properly installed at their facility. He asks you some questions to get to the root of the problem, and one shocks you: “What soap are you using to wash you truck?”

“Whatever is on sale at the local parts store,” you proudly and confidently respond.

“The soap you are using has destroyed your light lenses,” the manufacturer states. “What you are experiencing is environmental stress cracking, which is caused by exposure to chemicals.”

An Expensive Problem

A local department spent more than $2,000 in one year on damaged light lenses on just one piece of apparatus because of environmental stress cracking, or ESC. And in this economy in particular, there are better ways to spend a department budget, particularly when the problem is fully preventable.

ESC is one of the most -common causes of unexpected brittle failure of plastics, including polycarbonates. Exposure to liquid chemicals accelerates crazing, or the cracking of material in the glaze layer. ESC may account for between 15% and 30% of all plastic component failures in service.

It is somewhat different from polymer degradation in that stress cracking does not break polymer bonds. Instead it breaks the secondary linkages between polymers. In plain terms, the contact with various chemicals dramatically accelerates the degradation of plastics, causing cracking and the eventual failure of the plastic component.

A plastic material is any of a wide range of synthetic or semi-synthetic organic amorphous solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce costs.

A reagent is a "substance or compound that is added to a system in order to bring about a chemical reaction or is added to see if a reaction occurs." Such a reaction is used to confirm the presence of another substance.

What does ESC look like?

Environmental stress cracking looks like cracking — simple, right? This image taken at 2.3x magnification from a lens with ESC after being soaked in a seemingly mild vehicle wash.

Many of the apparatus and light manufacturers have identified this as a major problem; however, they have been at a loss as to how this problem should be addressed. In their defense, this is a little more complicated than just telling a customer not to use a certain brand of cleaning products. A manufacturer’s representative attempted to address this problem to their customers by telling them to stop using a certain brand product, only to find themselves threatened with legal action by the product’s manufacturer.

Apparatus and light manufacturers have identified this as a major problem; however, they have been at a loss as to how this problem should be addressed. In their defense, this is a little more complicated than just telling a customer not to use a certain brand of cleaning products. vA manufacturer’s representative attempted to address this problem to their customers by telling them to stop using a certain brand product, only to find themselves threatened with legal action by the product’s manufacturer.

One light manufacturer ESC in all but two of 12 soaps tested. The testing consisted of placing the soap on the lenses and waiting to see the reaction. Some of the samples caused cracking immediately, where other took several hours.

Apparatus manufacturers haven’t washed their hands of the issue by any means. A few have been actively working to resolve the problem. There was a recent Technical Bulletin sent out by FAMA, the trade organization of fire apparatus manufacturer’s regarding ESC. A few manufacturers are even looking into including a policy in their warranty related to vehicle washes and banning certain chemicals. One manufacturer stated in passing this might even be applied to their paint warranty.

This problem is not restricted to light lenses, but they are where the ESC is most evident. This could be related to the stress the lenses are under due to the importance of maintaining a tight seal to prevent water, dirt, dust, etc. from getting inside the light.

What to do about it?

How can you prevent ESC? I would like to say it is simple, but that is not the case. It will take diligence on your part as some of the manufactures of these products are not real forthcoming with information.

For example, a department recently e-mailed me regarding a particular soap and wanted my opinion. It seems they were having a difficult time getting any information on the soap. I told them to ask the simplest question anyone should be able to answer about their product: What is the pH? The answer shocked me.

The sales rep indicated a pH of between 7 and 11. That is like saying it has a pH somewhere between pure water and ammonia.

A third-party testing agency recently studied light lenses. The test involved using four identical samples of polycarbonate light lenses of a major light manufacturer. The lenses were exposed (soaked) to chemicals for a period of 24 hours. One lens was exposed to a popular truck wash (we will call lens A), which is readily available at many retailers. One lens was exposed to a vehicle wash designed for the public-safety industry (lens B). The third lens was exposed to water, as a control (lens C) and the fourth lens was not exposed to any liquid, another control (lens D).

The report indicates ESC was observed in the lens exposed to the popular wash, lens A within 2.5 hours. At the conclusion of the 24 hour test all lenses were examined and the only lens with any cracking was lens A. All lenses were examined under magnification and cracking was observed in lens A. whereas, no cracking was observed in any of the other lenses (B, C and D).

The vehicle washes used in the test will not be named in this article to maintain the integrity of this article. I will however state, the wash which caused the cracking is quite common and seemed to be quite mild. And the soap that caused no cracking is a product of a company that specializes in providing chemical solutions to the public-safety market.

Another interesting thing came out of this testing. The lead chemist who directed this test was so intrigued by the results he conducted extensive research and put together a vehicle wash policy.

Even following the policy might not be enough. Like I mentioned before it’s not that easy since many chemical manufacturers will not provide you with much in the way of information. It is up to you to decide if it is worth the risk. Another thing, if they have nothing to hide shouldn’t they give you the information? I guess you can infer noncompliance, if they are unwilling to provide information. In answer to our question regarding who pays to replace the lenses damaged by ESC, you do. ESC is not typically covered by a manufacturer’s warranty.

So after all of that, what do you take from this; adopt a chemical policy if not the one provided then develop your own. Make sure you do your research and use only products which do not contain any of the banned chemicals listed above.

Brad Kraut is a firefighter/EMT-B with more than 23 years experience. He currently serves with the Oconomowoc Fire Department and the Ashippun Fire Department. Kraut also is a safety team member with Road America and an adjunct fire instructor with Moraine Park Technical College.