Page 66 - OHS, June 2020

PPE: PROTECTIVE APPAREL
Why Do I Still Get Wet in My Waterproof, Breathable Rain Suit?
Just because you’re getting wet in your rain gear does not mean it’s ineffective. Here are some reasons, and solutions, for your rain gear selection process.
BY BRIAN NUTT
Basic question, right? I bought a rain suit to stay dry. I even spent the extra money to get one that is breathable, but sometimes, somehow, I still get wet. Is the rain suit leak-
ing? Should I send it back? What is going on? These are common issues with rain wear, and they happen whether the rain wear is breathable or not.
Before we get started, please keep in mind we are not talking about liquid chemical protection here— just rain. Most breathable products are not intended for chemical protection, but some are, so make sure you check with the manufacturer.
Understanding Breathability. First, it is impor- tant to understand what makes rain suits breathable. The most common method is to use a coating or lami- nate comprised of polyurethane or ePTFE (expanded Polytetrafluoroethylene) on the product that will keep large droplets of water out but also allow microscopic droplets to pass through. This process is referred to as Moisture Vapor Transmission (MVT).
How does this work? Can it also come in from the outside? Well, maybe if you are wearing the suit in a 100-degree rainstorm, but probably not. The coating allows water vapor to pass from the hot humid side (the interior of the suit close to the wearer), out to the cooler (exterior side). If you were to wear it in an environment that was hotter and more humid on the outside than the inside, the moisture could pass the other way. However, under those circumstances, you would be sweating so much it would not make sense to wear the rain suit at all.
Moisture Collection. Now that you understand a bit about how a breathable fabric works, here is how and why you can still get wet. The quick explanation is you are sweating too much or outworking the capacity of the coating to vent the moisture you are emitting. However, the answer could be a lot more than that. If you are sweating at all without the suit on, you are go- ing to continue and probably even perspire more with it on. No matter how breathable the fabric is, some of, and maybe a lot of, that moisture will collect. Just like working in a t-shirt on a hot day, there is no rain and no rain suit, but your shirt is wet. Again, the rule of thumb is that if you are already sweating before you put it on, plan on sweating more while you wear it.
Not only is your body emitting moisture, but it is also heating up the interior of the suit and creating a temperature differential that can cause condensation to form on the inside of the suit. Think of a cold drink in the summer and all the moisture that collects on the outside of the glass (condensation). It is not be- cause the glass is leaking, but rather that the glass is cooler and causes the humid air to collect on the sur- face as water droplets.
The same thing can happen in any rain suit, breath- able or not. Often times it is noticeable on a sweatshirt layered under a suit in the cold; the shoulders and back of the sweatshirt get damp because moisture is collecting on the inside and the sweatshirt is touching the suit in those locations and absorbing the moisture.
This does not mean a suit can never leak; when suits get older or have not been properly cared for, the
62 Occupational Health & Safety | JUNE 2020
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