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Selecting the Correct Shoecover

Shoecovers: How to Choose the Best Product for Your Cleanroom

Shoecovers are used in most controlled environments, though few operators who wear them give much thought to these essential critical environment consumables. A cleanroom spends an estimated 20 percent of its supplies budget on its operators’ disposable garments, including shoecovers, and there are misconceptions about which shoecover style are best for the controlled environment industry. After reading this white paper, many controlled environments might discover that they are using a shoecover that is not only inappropriate for their environment, but is more expensive than a better suited product.

With an understanding of the purpose of shoecovers and an awareness of the types of shoecover materials available, it can be assured that a cleanroom is using the best, cleanest and most appropriate product for its specific need.

Shoecovers: Materials and Background

Shoecovers were first introduced in the medical industry as a way to control foot-borne contamination in surgical rooms and hospitals. This shoecover is a non-woven material with a primary substrate of spun-bond polypropylene (SBPP). It offers an elastic ankle cuff, which makes it easy to slip on over a regular shoe. When the operator leaves the clean area, he or she removes the cover and throws it away.

Because SBPP has a smooth texture, there is a challenge to keep its wearer from slipping on

slick floor surfaces. In a hospital setting, this problem was easily solved by adding a coating of paint along the bottom of the shoecover, called a “tread.” Shoecovers with this tread are referred to as “anti-skid.”

When the controlled environment industry looked to controlling foot-borne contamination in its cleanrooms, it borrowed from an industry with similar products. However, polypropylene (PP) presents several problems in a controlled environment setting.  PP is a non-woven material, which means that it can and will shed particles. It also tears easily, increasing the shed particles, and it will absorb any moisture on the floor, increasing the possibility of tearing and creating a slip hazard for an operator.

In other words, though PP shoecovers prevent contaminants from a shoe worn outside the controlled environment from getting out into the cleanroom, it creates a contamination and safety hazard all its own. Anti-skid PP shoecovers compound this same problem: the paint coating can also shed. One only needs to check a critical environment’s prefilter to its HEPA (High Efficiency Particle Airflow) system or evidence of this particulation.

Polypropylene Shoecover Alternatives

The challenges critical environments face when selecting a shoecover include reducing the chance of creating more contamination with a particle-releasing material like SBPP, as well as increasing the safety of the operators by using an anti-skid tread.

  • Cleanroom Shoes

Cleanroom shoes are an option for environments looking to cut down on the waste created with disposable cleanroom garments and on particles generated from SBPP substrate shoecovers. Cleanroom shoes are designed for comfort, as they are made specifically for operators whom are often on their feet all day. They can be made ESD compliant, and slip on for ease of gowning. They will have slip-resistant soles and can be easily washed and wiped.

The cons associated with cleanroom shoes are cost and storage. The shoes can be upwards of $40 a pair, and must be stored within the clean environment; removing them from the cleanroom would defeat their purpose. Many controlled environments lack the space and funds to accommodate cleanroom shoes.

  • Polyethylene-Coated Polypropylene Shoecovers

These shoecovers attempt to protect against PP’s moisture-wicking trait by coating the PP material with polyethylene, a plastic-based substrate. This creates a more durable shoecover, one that won’t tear as easily as PP alone. However, this shoecover is created by laminating the plastic on the outside of the PP.  Because the substrates have different tensile strengths, the material will tend to delaminate during extended wear.

 

  • Cross-Linked Polyethylene Shoecovers

Considered one of the most economical options, non-particulating, extruded cross-link, 100-percent polyethelyne cleanroom shoecovers offer a solution to many of the problems created with SBPP shoecovers.

Constructed of a plastic-based substrate, cross-linked polyethelyne (CPE) shoecovers are cleaner, and the embossed pattern gives the bottom friction and makes them inherently anti-skid without the need for a coating that will particulate.   They last longer, as they are less prone to tearing than SBPP.   Available in three standard thicknesses (3,5,8 mil) these shoecovers can often be worn all day.  The heavyweight 8 mil can be worn multiple days, provided that it is properly stored in the gowning room.

The cons of CPE shoecovers are that the ankle cuff is placed in the center of the shoecover – not toward the back as with alternatives – creating a need for the operator to be re-educated as to why the change merits the effort required.

 

  • Polyethylene-Coated Polypropylene Shoecover with a PVC Sole

A coated polypropylene cleanroom shoecover with a PVC sole is considered the cleanest and most durable option in a disposable shoecover. It is also the most expensive option.

The PVC sole is durable, and its sticky texture makes it anti-skid, even on wet floors. The interior of the shoecover is comfortable polypropylene, the outside is coated with polyehtelyne to reduce particulation. These shoecovers are autoclavable and can be worn for up to a week.

Conclusion

There are several factors to consider when finding the appropriate cleanroom shoecover for an environment’s needs: comfort, safety, cost and cleanliness. Each controlled environment must assess all of these when making a decision about the shoecover best suited for its needs.

Download a copy of “Shoecovers: How to Choose the Best Product for Your Cleanroom

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