Recognizing and Protecting Against the Dangers of Footwear Degradation

Under-performing footwear can lead to serious workplace safety risks.

By: Robert McCarthy, Contributor

Worker standing on harsh, metal gaiter flooring in a warehousing environment, wearing the Women’s Rainier 6” NVT. Image courtesy of Shoes For Crews.

We have all encountered a situation where the shoes we wear daily for work start to wear out. Whether it’s losing outsole traction or the leather upper starting to crack, wearing shoes that have begun to break down can be dangerous. Footwear degradation can contribute to slips, trip, falls and other health and safety risks.  In fact, the Bureau of Labor Statistics reported more than 211,000 nonfatal slips, trips and falls[1] resulting in days away from work in all sectors in 2020. And according to the agency’s Census of Fatal Occupational Injuries, work related fatalities[2] due to falls, slips, and trips increased 5.6 percent in 2021, from 805 fatalities in 2020 to 850 in 2021.

When workplace footwear performs at its highest level, it provides comfort during long days, empowers prolonged foot health, and protects against occupational hazards. But when it begins to degrade and break down, it goes from being an important safety measure to a serious risk, leading to discomfort and potential accidents. To mitigate the harmful effects of slips, trips, and falls, as well as other workplace dangers that may be attributable to under-performing footwear, two critical questions must be answered:

• Are these shoes constructed properly with suitable materials for the job and the environment?
• How should they be maintained and stored to prolong their useful life and protective qualities?

Materials, construction, and performance properties can all be compromised by time and aging, environmental conditions and daily wear and tear. Below, we’ll look at the impact of various factors, including time, environment and storage habits, on the effectiveness of safety footwear and how to counteract them.

How Time and Environmental Conditions Impact Leather

Leather is the preferred material for footwear worn in industrial environments. Leather is produced by tanning animal hides, resulting in a more porous and fibrous finished product. In shoe construction, leather offers several important qualities for the wearer, including breathability and high tensile strength. Leather can also absorb moisture, and exposure to high humidity levels can seriously damage leather and cause it to break down. A study[3] by the Society of Leather Technologists and Chemists (SLTC) found that “leather is strongly affected by three main environmental parameters – temperature, relative humidity, and UV radiation.” These factors are not only present in the workplace while wearing the shoes; they can impact how and where footwear is stored between shifts.

Damp, humid conditions can cause hydrolysis, the chemical breakdown of a compound as a reaction to water. Hydrolysis is more common in leather boots worn in wet, muddy, or contaminant-rich environments, especially if they aren’t cleaned immediately or are stored in confined spaces, like lockers or closets, while damp. This practice can also promote mold growth. Wearing leather footwear in high-humidity conditions, under the constant stress of flexing, load-bearing, kicking pallets and other activities common to various industrial settings, can accelerate material breakdown in areas such as the flex point where the upper meets the midsole at the ball of the foot.

Oxidation is another common issue and a significant concern for the wearer. A study published by the Heritage Science Journal found that “oxidation causes weakening of physical stability of leather. The rate of this process increases at higher temperatures and lower relative humidity, light, and presence of air pollutants.” While oxidation is a natural process that cannot be eliminated, its effects can be slowed through proper cleaning and maintenance procedures. Like hydrolysis, it also must be considered when storing one’s footwear during periods of non-use at home.

Beyond the impact of hydrolysis and oxidation, exposure to abrasive flooring or other rough surfaces can lead to wear and tear of shoe uppers, especially if the toe is exposed. Safety footwear manufacturers increasingly use durable rubber or thermoplastic polyurethane (TPU) to reinforce the toe cap in one’s boots and provide an extra protection layer. Even when footwear contains an underlying, protective steel safety toe cap, it is dangerous to wear any shoe with compromised leather or safety toe exposure, particularly in an industrial workplace, and safety managers should restrict employees from doing so.

It is essential to recognize that the integrity of safety footwear can also be compromised by dry conditions, which can cause the leather to crack and lose its tensile strength. Small cracks can grow over time, allowing dirt, mud, and harmful contaminants to destroy the shoe’s structural integrity.

What About the Rest of the Shoe?

Worker in a wet environment, wearing the Glacier NCT WP boot. Image courtesy of Shoes For Crews.

While leather is used in most safety footwear, other materials can often be found in boot uppers, midsoles, and reinforcements, each presenting benefits and challenges. Liquid-resistant pull-on boots, for example, can be made of leather alternatives like polyurethane (PU), polyvinyl chloride (PVC), or rubber, each with varying degrees of chemical protection, flexibility, cushioning, traction and life span.

PU is lightweight, thermo-insulating, easier to clean, highly versatile, and environmentally friendly, but it does not have the same capabilities or durability as genuine leather. PVC is durable and has good resistance to cold, but it is heavier and less flexible than PU when used as an upper material. On the other hand, rubber provides resistance to things like animal fats and blood, oils, certain acids, alkalis and alcohols and contains plasticizers to maintain flexibility; however, these plasticizers or resins can leech and cause brittleness under continued hot conditions.

Adhesive strength in cement-constructed footwear, such as the bond between the upper and midsole or midsole and outsole, can weaken with daily wear or exposure to adverse conditions, like heat. Commonly used midsole materials include ethylene-vinyl acetate (EVA), PU, and TPU. Although EVA provides lightweight cushioning and can be compressed and molded into contoured shapes, it is subject to compression set over time, where its rebound properties are reduced, putting undue pressure on the joints and contributing to plantar fasciitis, shin splints, and other painful chronic conditions.

PU is typically lightweight, flexible and resilient but susceptible to the effects of hydrolysis. Despite the use of stabilizers in PU manufacturing, moisture exposure — even while in storage — can accelerate degradation and cause the midsole to crack and crumble. TPU is similarly considered sturdy when used as an outsole material and has relatively strong abrasion and slip resistance. However, it can suffer the same pitfalls as PU when subjected to hot, humid conditions.

Always Be Prepared

Footwear maintenance is not an exact science, and there is no consistent timeline for how and when footwear can break down and see its performance properties compromised. Protecting against the unpredictability of safety footwear degradation means diligently monitoring environmental conditions and tracking daily wear. As signs of wear become noticeable, footwear must be replaced. We all have our old, reliable shoes we’ve worn for years, but as familiar and comfortable as they seem, they might not provide adequate protection in the workplace. Consider swapping that old pair for a new one with appropriate protections, renewed comfort, and enhanced slip resistance — you’ll be glad you did. WMHS

Robert (Bob) McCarthy is Associate Director of Product Marketing for Shoes For Crews, LLC. In his 32 years in the footwear industry, he’s had the opportunity to observe workers in various environments, conduct marketplace research, and collaborate with Safety and Risk Managers, in addition to managing product and process. Learn more at www.shoesforcrews.com.

[1] “Bureau of Labor Statistics Data.” U.S. Bureau of Labor Statistics. Accessed October 26, 2023. https://data.bls.gov/timeseries/CSU00X4XXXXX6E100.

[2] “Census of Fatal Occupational Injuries Summary, 2021.” Bureau of Labor Statistics, December 16, 2022. https://www.bls.gov/news.release/pdf/cfoi.pdf.

[3] Anna Bacardit, Taimoor Mir, Joaquim Font, Rosa Cuadros, L. Ollé.  “Effect of Temperature, Relative Humidity and UV Radiation on Wet-Bright Leather Aging.” Journal of the Society of Leather Technologists and Chemists (2017). https://www.researchgate.net/publication/320693883_Effect_of_temperature_relative_humidity_and_UV_radiation_on_wet-bright_leather_ageing. (sic)