Measuring the Effectiveness of Protective Clothing
by Deborah Davis, MS, MBA
Barrier protection was once intended to prevent infection from being transmitted from clinical practitioner to patient. Today, this protection is required for both healthcare workers and their patients. Availability of personal protective equipment (PPE) is mandated by the Occupational Safety and Health Administration (OSHA). These requirements are detailed in the OSHA standard on Occupational Exposure to Bloodborne Pathogens, which went into effect March 6, 1992, and include the implementation of the Centers for Disease Control and Prevention's (CDC) universal precautions. Universal precautions (standard precautions in CDC's 1996 guidelines) as defined by CDC are a set of actions that involve the use of protective barriers, such as gloves, gowns, aprons, masks, or protective eyewear, to reduce the risk of exposure of the healthcare worker's skin or mucous membranes to potentially infective materials.
The Center for Devices and Radiological Health, Food and Drug Administration (FDA) has responsibility for regulating medical devices. Products, such as gloves, are required by the FDA to meet certain performance requirements. These requirements define performance properties, such as the minimum strength, barrier protection, and fluid resistance, that these products must exhibit. For surgical gowns, the only required test is for flammability. If specific advertising and labeling claims are made, then the corresponding standard must be met.
Manufacturers of PPE conduct extensive testing during product development and during ongoing quality control procedures to assure that their products meet the demanding performance requirements of today's healthcare environment. Understanding the significance of these tests can help clinicians assess the performance of each product as well as its appropriate usage. Barrier effectiveness can be defined as the ability of PPE to withstand rigorous physical testing and bacteriophage penetration testing and to resist fluid penetration under pressure. The efficacy of the barrier should not be compromised by the procedure being performed. Standards and test methods may be developed by organizations such as the American Society of Testing and Materials (ASTM), the Association of Non-Woven Fabrics Industry (INDA), the American Association of Textile Chemists and Colorists (AATCC), and various international groups. Typically, these organizations are made up of scientists and engineers who have knowledge and experience in the behavior properties of the materials, the manufacturing processes, and the testing methodologies. Some of the organizations develop test methods and standards based on a consensus approach, which helps ensure that the tests are not only scientifically sound and appropriate but also that the test methods fairly and accurately assess products made from a variety of manufacturing approaches, formulations, and materials.
For the most part, test methods are available for measuring clothing performance for several properties within each performance area (i.e., pull strength as well as tear strength). The selected test methods should mirror expected-use conditions (allowing for a margin of safety by simulating worst-case conditions) or at least rank clothing consistent with in-use performance. Performance limits may be set in conjunction with the test methods. For example, chemical protective gloves may be used against chemical "X" for a one-hour period. Selecting a chemical resistance test method and a requirement for chemical holdout is one way of judging acceptable performance. Performance limits may sometimes be set by comparing results for an item of PPE that has already provided satisfactory performance. If the test method already has a pass/fail requirement, the conditions that lead to this determination need only be examined for their relevance to the situation at hand.
Barrier Protection Confidence
Acceptable Quality Level (AQL). This typically refers to the barrier protection confidence level. A lower AQL number represents a higher quality product, i.e., a manufacturing process with fewer allowable defects. For purposes of sampling inspection, the AQL is used by manufacturers to identify the maximum number of allowable defects (pinholes) per hundred units. All gloves must be statistically sampled to verify the attainment of specific AQLs.
The 1000 mL water leak test and/or air inflation test is typically used to verify the AQL.
Water Leak. Consists of filling the glove with 1000 mL of water, suspending it, and allowing it to hang for two minutes then inspecting it for any leakage (ASTM D5151).
Air Inflation. Consists of inflating the glove with compressed air and visually inspecting for holes.
Chemical Permeation. This test method measures the resistance of protective clothing materials to permeation by liquid or gaseous chemicals under conditions of continuous contact (ASTM F739).
PPE is designed to protect the wearer from exposure to a variety of potentially hazardous fluids and other materials. Effectiveness is measured in several ways.
Gowns and Drapes
Water Impact. A measurement of a fabric's resistance to the penetration of water by impact, which indicates performance when fluid falls onto the fabric. Lower numbers reflect superior performance (AATCC 42).
Mason Jar. A measurement of the resistance of a fabric to an aqueous solution under constant pressure, which indicates performance when fluid remains standing on an area of the fabric. Higher numbers reflect superior performance (IST 80.5).
Hydrostatic Head. A measurement of the resistance of a fabric to an aqueous solution under constantly increasing pressure, which indicates performance when fluid is accumulating on the fabric. Higher numbers reflect superior performance (AATCC 127).
Alcohol Repellency. A measurement of a fabric's resistance to aqueous isopropyl alcohol solutions, which indicates the fabric's barrier capabilities to alcohol solutions. Higher numbers reflect superior performance (IST 80.8).
PPE comes under quite a bit of stress during its actual usage. Product strength is measured by its resistance to tearing, puncturing, and breaking and by its ability to stretch.
Tensile Strength. Measures how much force, in pounds per square inch, is required to stretch a sample of glove until it breaks. Higher numbers reflect superior performance.
Elongation. Measures how far, as a percentage of the original sample length, the glove stretches before it breaks. For example, if a 1" sample stretches 9" before it breaks, the elongation is 900%. Higher numbers reflect superior performance.
V-Tear. Measures the force in pounds per square inch necessary to start a tear (ASTM D412).
Trouser Tear. Measures the force (pounds per square inch) necessary to continue tearing once an initial tear has been made (ASTM D412).
Gowns and Drapes
Mullen Burst. A measurement of a fabric's resistance to puncture under increasing pressure. Higher numbers reflect superior performance (ASTM D744).
Grab Tensile. A measurement of a fabric's resistance to tearing under increasing pulling stress without an initial tear in the material. Higher numbers reflect superior performance (ASTM D5034).
Elmendorf Tear. A measurement of a fabric's resistance to tearing under controlled force when there is an initial tear in the material (ASTM D1424).
All fabrics used in surgical gowns and drapes can burn. Manufacturers of gowns and drapes incorporate a caution label on the package warning that the fabric can burn in the OR.
The rate of flame travel will vary with the specific material and can be measured using a standard test method described in the Consumer Products Safety Commission (CPSC) 16 CFR part 1610. This measure is the basis for the separation of various fabrics into three classes of flammability. Class I represents "normal flammability" or a flame spread time of 3.5 or more seconds.
Medical gloves, drapes, and gowns are required to undergo a variety of tests that demonstrate the potential of the material to cause irritation to the skin. These tests include:
- cytotoxicity (cell culture)
- primary skin irritation (demonstrates the potential for irritating abraded skin)
- dermal sensitization (demonstrates the potential for eliciting allergic contact dermatitis)
While barrier effectiveness is foremost, if PPE is uncomfortable to wear, it is less likely to be used effectively. The discomfort may even interfere with the clinician's ability to do his or her job.
Tensile Stress (Modulus). Measures how much force, in pounds per square inch, is required to stretch a sample of glove twice its length. This is a measure of comfort; lower numbers reflect a softer, typically more comfortable glove.
Gowns and Drapes
Air Permeability. A measurement of the air flow that can be maintained through a material at a specified pressure, which indicates the fabric's breathability and comfort during use. Higher numbers reflect superior performance (ASTM D737).
Handle-O-Meter (Stiffness). A measurement of the force of a fabric's resistance to flexing (i.e., folding or draping). The higher the force, the stiffer the fabric (IST 90).
Protection Against Microorganisms
While fluid repellency and barrier tests are excellent indicators of PPE's performance, there is also testing, which more specifically demonstrates a material's ability to prevent penetration by microorganisms.
Bacteriophage penetration resistance is a test method that assesses the effectiveness of materials used in protective clothing for preventing the penetration of a surrogate microbe (Phi X 174 bacteriophage) suspended in a simulated body fluid under conditions of continuous contact. This is a pass/fail test (ASTM F1671).
How the product is stored can affect the polymers and fabrics used in the products and, therefore, adversely affect barrier properties. Products should be stored in their original packaging in cool, dry environments and away from UV or fluorescent lights to help ensure the barrier effectiveness stability during storage. Stock should be rotated on a first in, first out basis.
Using Product Performance Testing to Your Advantage
Infection control is a vital concern in healthcare today. Intelligent and informed use of PPE is a critical component of your facility's infection control program. Understanding the standards and tests that are used to measure the performance of this equipment will allow you to choose equipment that provides the best barrier protection and performance for both healthcare workers and their patients.
Deborach Davis, MS, MBA, is Technical Director for the Gloves business unit of Allegiance Healthcare Corporation (McGaw Park, Ill). Her primary responsibilities include driving clinical research initiatives; coordinating various aspects of product development between the marketing, regulatory, manufacturing, and research and development organizations; and publication and presentation of technical information for customers and field sales personnel.
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