Workers meticulously inspect their steel-toe boots for crushed toes and their safety glasses for deep scratches. However, two of the most common PPE failures are caused by invisible chemical and structural degradation that occurs off the job site: Polyurethane (PU) Hydrolysis in safety footwear and Chemical Stress Cracking in polycarbonate safety eyewear.
The Footwear Failure: Many modern, lightweight safety boots feature midsoles and outsoles made of Polyurethane (PU). PU is an incredible shock absorber, but it is a porous polymer. When boots are stored in dark, damp environments (like a locker, a wet truck cab, or a basement), the moisture absorbs into the PU matrix. Through a chemical process called hydrolysis, the water molecules react with the polymer bonds, breaking them down. Over 12 to 18 months of improper storage, the PU turns into a dry, crumbly powder. A worker steps onto a concrete floor, and the sole literally disintegrates into chunks, twisting their ankle and destroying their footing.
The Eyewear Failure: Polycarbonate is the standard for impact-resistant safety lenses, but it is highly vulnerable to solvents. In the summer, workers spray their hard hats and necks with insect repellent containing DEET, or they use industrial hand sanitizers and wiping compounds. When DEET or strong alcohols touch the polycarbonate lens, it doesn't just smear; it attacks the polymer surface, causing rapid evaporation that cools the surface unevenly. This creates "crazing"-a network of microscopic cracks across the lens. Crazed lenses shatter upon high-velocity impact, turning protective eyewear into blinding shrapnel.
The Maintenance Protocol:
Boots: Never store PU-soled boots in sealed lockers or damp environments. Remove the insoles, stuff the boots with newspaper to absorb internal moisture, and store them in a dry, well-ventilated area with low humidity to halt the hydrolysis reaction. If the sole feels unusually light, chalky, or flakes when you press it with your thumbnail, the boots are structurally dead.
Glasses: Never apply insect repellent or hand sanitizer while wearing your safety glasses. If DEET or solvents contact the lens, immediately flush them with copious amounts of clean water-do not wipe them dry, as the cloth will drag the solvent deeper into the crazing. If a lens looks hazy or has a spiderweb of fine lines when held under a bright light, it has lost its impact rating and must be thrown away.
