A full-body safety harness is the last line of defense between you and a fatal fall. Because of this, safety regulations are very strict about their lifespan, usually mandating that a harness be taken out of service after five years, regardless of how it looks. But what the regulations don't always emphasize is that a harness can easily degrade to a dangerous level long before that five-year mark if it spends its life in the back of a work truck. The enemy here isn't massive rips or frayed edges; it is silent chemical degradation.
Most workers know not to throw a harness in a pile of spilled paint thinner or battery acid. But they don't realize that the synthetic webbing-usually nylon or polyester-is highly susceptible to ultraviolet light and exhaust fumes. Leaving a harness draped over the seat of a truck cab, where the sun bakes it through the windshield every afternoon, does massive damage to the fibers. UV light breaks down the molecular bonds in the nylon, causing it to become brittle and lose its tensile strength. It might look perfectly black and intact, but under a microscope, the fibers are dry and cracked.
Polyester handles UV light much better than nylon, but polyester has its own kryptonite: acid. If a worker is wearing a polyester harness in an environment with high chemical exposure, or even just around the diesel exhaust of heavy machinery, the fibers can weaken without showing any outward signs of damage.
This is why the pre-use inspection of a harness has to go far beyond a casual glance. You cannot just look at the webbing; you have to feel it. Take the chest strap and the leg straps between your fingers and bend the webbing back and forth aggressively. If the fibers are degrading, you will feel a slight crunchiness, or you will see tiny white dust particles falling out of the weave. That dust is dead synthetic fiber. If you see dust, or if the webbing feels unusually stiff compared to a brand-new harness, it is done. It has to be cut up and thrown in the trash so nobody else is tempted to use it.
You also need to pay close attention to the stitching. The heavy box stitching at every D-ring and buckle connection point is the most vulnerable part of the harness. Even if the main webbing is fine, if the thick tension-bearing threads at the D-rings are sun-bleached, frayed, or pulled, the entire harness will fail exactly where it is supposed to hold the most weight. Store your harness in a cool, dry, dark bucket or bag when you aren't wearing it. Don't leave it out to bake in the sun like a piece of construction equipment. It is a life-support device, and it needs to be treated like one.
