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Biomechanical performance of powder-free examination gloves1
The Journal of Emergency Medicine, Vol. 17, No. 6, pp. 1011–1018, 1999 Copyright © 1999 Elsevier Science Inc. Printed in the USA. All rights reserved 0736-4679/99 $–see front matter
PII S0736-4679(99)00133-X
Selected Topics: Wound Care
BIOMECHANICAL PERFORMANCE OF POWDER-FREE EXAMINATION GLOVES Mark D. Fisher, BA,* Vikram R. Reddy, BA,* Freddie M. Williams, BA, Kant Y Lin, John G. Thacker, PhD,† and Richard F. Edlich, MD, PhD*
MD,*
*Department of Plastic Surgery, University of Virginia School of Medicine and †Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia Reprint Address: Richard F. Edlich, MD, PhD, Department of Plastic Surgery, University of Virginia School of Medicine, Box 332, Charlottesville, VA 22908
e Abstract—Biomechanical performance studies were undertaken for powder-free, latex and nitrile examination gloves. Using standardized tests, examination glove performance was judged by measuring glove thickness, glove puncture force, glove tape adhesion force, glove donning force, glove stiffness, and immediate unrecovered stretch. Even though the nitrile examination gloves were thinner than the latex examination gloves, they exhibited a greater puncture resistance. In addition, tape adherence to the N-Dex™ nitrile glove was the lowest. Moreover, measurements of the handling characteristics of the nitrile examination gloves demonstrated that they are an acceptable alternative to latex examination gloves. While these biomechanical studies demonstrate the superiority of the nitrile examination gloves, clinical glove evaluation is still needed to determine their performance in the health care setting. © 1999 Elsevier Science Inc.
Disease Control and Prevention (1). The premise of universal precautions is that every specimen should be handled as if it came from someone infected with a blood-borne pathogen. All hospitals are mandated by the Occupational Safety and Health Administration (OSHA) to provide annual in-service training in, and to monitor compliance with, universal precautions to protect health care workers from blood-borne pathogens, including human immunodeficiency virus (HIV) and hepatitis B and C viruses. OSHA requires the employer to provide, at no cost to the employee, personal protective equipment, including gloves, to protect the employee against exposure to blood-borne pathogens (2). In addition, the National Fire Protection Association (NFPA) offers specific performance criteria involving glove exposure to surrogate virus challenge (3). Since the advent of universal precautions, latex gloves have been routinely used to protect health care workers against blood-borne pathogens. The frequency of latex glove usage increased dramatically, from 1 billion gloves in 1987 to 10 billion in 1996 (4). This dramatic increase in latex glove usage is associated with an increase in the frequency of latexallergic reactions in health care personnel that has reached epidemic proportions. The cornstarch powder on the surface of latex gloves has been shown to bind with the latex antigens and serve as a vector for this epidemic (5). In addition, the corn-
e Keywords—latex gloves; nitrile gloves; glove thickness; glove puncture resistance; glove stiffness; glove tape adherence; glove donning force; immediate unrecovered stretch
INTRODUCTION Health care workers in the Emergency Department (ED) as well as in prehospital treatment routinely wear examination gloves. This is consistent with the universal precautions instituted and recommended by the Centers for
Selected Topics: Wound Care is coordinated by Richard F. Edlich, MD, PhD, of the University of Virginia Medical Center, Charlottesville, Virginia
RECEIVED: 25 January 1999; FINAL ACCEPTED: 25 May 1999
SUBMISSION RECEIVED:
19 April 1999; 1011
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starch powder has been shown to be damaging to tissues (6). Consequently, many glove manufacturers are now manufacturing powder-free, latex-free synthetic examination gloves whose sizes correspond to the manufactured latex examination gloves. Because emergency medical personnel often do not know if their patients are sensitized to latex antigens, emergency health care workers are advised to wear latex-free, powder-free examination gloves. Some emergency medical personnel are now using these new powder-free, latex-free examination gloves in emergency medical systems throughout the country. These examination gloves are manufactured as nonsterile gloves designated for single-use only. The manufacturers provide the gloves in five sizes (extra small, small, medium, large, and extra large) and in ambidextrous sizing. To be labeled or otherwise represented as being compliant with NFPA 1999 standards, the gloves must meet or exceed all applicable requirements specified in this standard and be certified as such (3). Because many emergency medical personnel are still not familiar with these new powder-free, latex-free examination gloves, we undertook this study to compare the biomechanical performance of latex-free, powderfree examination gloves with that of a powder-free, latex examination glove. The performance of these different examination gloves was evaluated by standardized measurements that included the following parameters: thickness, puncture resistance, glove tape adhesion force, glove donning force, glove stiffness, and immediate unrecovered stretch.
MATERIALS AND METHODS Examination Gloves Three different commercially available powder-free examination gloves were evaluated in this study. The Best N-Dex® glove (Best Manufacturing Co., Menlo, GA) is a nitrile examination glove that is enclosed in a box with a label signifying that the glove complies with the NFPA 1999 Standard on Protective Clothing for Emergency Medical Operations (3). The Safeskin® nitrile examination glove (Safeskin Corp., San Diego, CA) is a powderfree nitrile glove. The Safeskin® PFE (powder-free examination) glove is made of powder-free latex. The gloves are packaged in a box with a label stating that the glove contains reduced levels of natural rubber latex proteins, containing 50 micrograms or less of total waterextractable protein per gm using the ASTM D 5712 Test (7). All three types of gloves tested were medium size, ambidextrous, and clean but not sterile.
Biomechanical Performance The biomechanical performance of the powder-free nitrile and latex gloves was determined by standard tests that measured glove thickness, glove puncture resistance, glove tape adhesion force, glove donning force, glove stiffness, and immediate unrecovered stretch.
Glove Thickness The thickness of each glove was measured using a spring-loaded micrometer. When measuring the thickness of the gloves, the spring-loaded micrometer and pad loaded the membrane with a compressive force of 14.6 kPa (2.1 lb/in (2). These measurements were made at the tip of the index finger for 10 different gloves of each brand. The data were reported as the average fingertip thickness for 10 different index glove fingertips.
Puncture Resistance The glove puncture resistance test was performed in accordance with American Society of Testing and Materials (ASTM) F 1342–91 (reapproved 1996) (8). This test has been incorporated as one of the standards of the NFPA 1999 Standards for Gloves. The test uses a metal puncture probe whose diameter is comparable to that of the end of a nail. Jackson et al. reported that the magnitude of the glove penetration forces for an 18-gauge hypodermic needle was significantly less than those for the metal penetrometer (8). Because our petition to the ASTM and NFPA to add the hypodermic needle test to the standard penetrometer probe test has not been approved by these organizations, we continued to employ the metal penetrometer probe test as the standard measure of glove puncture resistance in this study. A glove sample is placed in a stationary support assembly that is in turn affixed to the lower arm of a tension testing machine. A stainless steel pointed puncture probe is specially made to conform to set dimensions. This puncture probe is mounted to the penetrometer stand, and the whole assembly is attached to the compression cell of the Instron® Model 1222 (Instron Corp., Canton, MA). The puncture probe moves at a constant velocity until it punctures the material specimen. The force required to puncture the material specimen is measured by the compression cell. The testing machine is calibrated so that the error of the machine does not exceed 2% at any reading within its loading range. The specimen support assembly consists of two flat metal specimen support plates that clamp together. The
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Figure 1. The thickness of the nitrile examination gloves was significantly lower than that of the latex gloves.
sample specimen is held tightly between them, straining the glove specimen with a uniform movement of the pulling clamp. The two specimen support plates are connected to the testing machine using a machine interface plate. Each plate has 24 0.6 cm (1/4 in) diameter holes, located 1.9 cm (3/4 in) from the plate edge. Samples of the gloves are taken from the tip of the index finger and the specimen to be tested is placed in the support assembly. The reported puncture resistance is determined by the average of 10 tests. The two plates are marked and the holes are aligned before testing to avoid damaging the penetrometer and plates. The material support assembly is attached to the compression cell of the test apparatus and the puncture probe is positioned on the moveable arm of the Instron® tensile tester. The testing machine is set such that the penetrometer has a velocity of 50.8 cm/min (20 in/min) under load conditions and is uniform at all times. The penetrometer stops and retracts when it has punctured the sample specimen. The compression cell measures the maximum puncture resistance, and the results are recorded as the maximum puncture resistance in grams with a strip chart recorder and expressed in Newtons. If the sample specimen has not been penetrated, a maximum force of 23 kg (50 lb.) will be recorded. After each test is completed, the penetrometer is repositioned above each of the remaining guide holes and the test is repeated.
Glove Tape Adherence The adhesion of tape to surfaces is determined by peel adhesion (9). Peel adhesion is the force necessary to peel the tape from a surface, under standard conditions, at a specified rate and angle of pull (10). The tape used is a 6 mm ⫻ 10 cm Steri-Strip™ (3M Center, St. Paul, MN). Each tape sample is uniformly applied to the specified surface. The pressure of application is standardized by rolling a 1-kg weight across each tape. Peel adhesion measurements are made approximately 5 min after tape application. Each tape contained, for testing purposes, a 1/4 in tab that did not adhere to the specified surface. The level of adhesion is measured by clipping the exposed end of the tape to the Instron® Model 1123 tensile tester. The tape is then peeled from the specified surface at 100 mm/min, while measuring the force required to remove the tape.
Glove Donning Force One experiment was conducted to examine the forces required to don the three different brands of gloves with dry hands. A glove donning load tester was constructed consisting of a ring assembly with two tapered rings (diameter 125 mm) between which the cuff of the glove was secured (11). This ring assembly was attached to a rigid base that was set upon a calibrated scale. Each
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Figure 2. The puncture resistance of the nitrile examination gloves was nearly twofold greater than that of the latex examination gloves.
Figure 3. The N-Dex™ nitrile examination gloves exhibited the lowest adherence of tape.
Examination Glove Performance
subject with appropriately sized medium hands inserted a hand into a medium glove, while the maximum force required to don the glove was reproducibly measured and recorded on a strip chart recorder. As the eight volunteers performed the trials, they were trained to achieve uniformity in donning angle and the time to don with minimal movement during insertion into the glove. First, each subject was asked to don each of the three brands of examination gloves with dry hands. After donning each glove, the subject’s hand was washed and then dried to remove any surface lubricant or detergent. The order in which the gloves were donned was randomly assigned.
Glove Stiffness Curves expressing the relationship of elongation to force for each of the gloves were produced by stretching samples with an Instron® Model 1123 tensile tester and recording the forces with a strip chart recorder in gm and expressed in Newtons. Sample strips 2.5 cm wide were cut from the tubular area of the gloves close to the cuff. The strips were then pneumatically clamped into the moving cross-arm and load cell clamps of the Instron® tester. The gauge length, the distance between the two clamps of the sample, was 10 cm. The cross-arm speed was 5 cm/min, and the strips were stretched 2.5 cm. The forces required to stretch each of the samples 2.5 cm were used to calculate glove stiffness values for the three gloves. Stiffness was calculated by multiplying the stretch force by the length of stretch.
Immediate Unrecovered Stretch Recovery is the degree to which the glove samples were able to return to their original length after being stretched. To determine the recovery of the different gloves, each glove sample was first stretched 2.5 cm, after which tension was allowed to return to zero. The load and extension were graphically displayed. Data were collected from the graphically plotted data to calculate total change in sample length immediately after being stretched. The immediate unrecovered stretch was measured as the difference between the initial upload asymptote intercept and the initial download asymptote intercept at zero load and expressed in millimeters.
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Statistical Analysis of Data These data were first analyzed by using an ANOVA method to assess the statistical significance of each biomechanical parameter (12). A statistically significant difference in these measurements was confirmed (p ⬍ 0.05). A Duncan’s test was then used to statistically separate the gloves into groups.
RESULTS The Safeskin娂 latex gloves were thicker than the nitrile gloves (p ⬍ 0.05) (Figure 1). In contrast, the N-Dex娂 glove was significantly thicker than the other nitrile glove (p ⬍ 0.05). An analysis of variance confirmed that there were significantly different puncture resistant forces for the three examination gloves (p ⬍ 0.05) (Figure 2). The puncture resistance of the nitrile gloves was more than twofold greater than that of the latex gloves (p ⬍ 0.05). The puncture resistance of the nitrile gloves did not differ significantly. It is important to emphasize that the puncture resistances of the two nitrile gloves comply with the NFPA Puncture Resistance Standard of 4.45 N (3). The peel adhesion of microporous tape to the NDex娂 nitrile gloves was significantly lower than that encountered with any other examination glove (p ⬍ 0.05) (Figure 3). The peel adhesion to the Safeskin娂 Latex and Safeskin娂 nitrile gloves was nearly twofold and fivefold greater, respectively, than that found with the N-Dex娂 nitrile gloves. The glove handling characteristics were judged by the following parameters: glove donning forces, glove stiffness, and immediate unrecovered stretch. The glove donning force encountered with the latex examination gloves was the lowest but did not differ significantly from those found with the nitrile gloves (Figure 4). It is important to emphasize that all the gloves could be donned without tearing the glove. The stiffness of the Safeskin娂 nitrile gloves was significantly greater than that of any other examination glove (p ⬍ 0.05) (Figure 5). The stiffness of the N-Dex™ nitrile gloves did not differ significantly from that of the latex glove. There were noticeable differences among the gloves in terms of immediate unrecovered stretch, or length of change of sample after being stretched 2.5 cm (Figure 6). The glove sample with the least change in length after being stretched and returned to zero tension was the Safeskin娂 latex glove (p ⬍ 0.05). The N-Dex娂 nitrile glove had the second lowest value for immediate unrecovered stretch, followed by the Safeskin娂 nitrile glove.
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Figure 4. The glove donning forces for the examination gloves did not differ significantly.
Figure 5. The stiffness of the latex and N-Dex™ nitrile examination gloves were the lowest.
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Figure 6. The latex examination gloves had the lowest immediate unrecovered stretch.
DISCUSSION It is important to emphasize that the N-Dex娂 nitrile glove is the only examination glove tested that is certified to comply with NFPA 1999 Standards on gloves for emergency medical operations (3). Gloves in boxes labeled NFPA compliant meet the emergency medical glove requirements established by the NFPA 1999. All sample gloves are tested for watertight integrity and must have an acceptable quality limit of 1.5% leakage or better. Glove material samples shall exhibit no penetration of Phi-X-174 bacteriophage for at least 1 h. In addition, glove material samples are tested for ultimate elongation following heat aging and isopropanol immersion. The N- Dex™ nitrile glove, as well as the other nitrile glove which is not certified by NFPA 1999 Standards, have some unique advantages over latex gloves. Their resistance to puncture is more than twofold greater than that encountered with the latex gloves. In addition, the nitrile gloves are thinner than the latex gloves. There was one notable advantage of the N-Dex™ nitrile glove over that of the Safeskin™ nitrile glove: The adhesion of tape to the Safeskin™ nitrile glove was fivefold greater than to the N-Dex™ nitrile glove. Tape adherence to gloves is an extremely important consideration when emergency medical personnel use adhesive tape for securing bandages, i.v. lines, and tubes. An understanding of the handling characteristics of
examination gloves can be especially challenging because they are manufactured as ambidextrous gloves in only five sizes. Consequently, they are not designed to be form-fitted, like surgical gloves manufactured in half sizes from 5 to 9. Measurement of the glove donning forces demonstrated that all latex and nitrile examination gloves can be donned without tearing. The glove donning forces for the latex gloves are lower than those for the nitrile gloves, but do not differ significantly. The stiffness of the N-Dex™ nitrile gloves is remarkably similar to that of the latex gloves. The stiffness of the Safeskin™ nitrile glove is significantly greater than that of the other examination gloves. The immediate unrecovered stretch for the latex gloves is lower than those of the nitrile gloves. After the latex gloves were stretched and tension removed from the gloves, the latex gloves returned to their original dimensions. In contrast, the nitrile gloves elongated after stretching once the tension was reduced to zero. These measurements are consistent with the clinical observation that nitrile gloves will comfortably elongate over the wearer’s hands. In contrast, latex gloves resist elongation, applying continuous pressure to the wearer’s hands. These biomechanical measurements of glove donning forces, glove stiffness, and immediate unrecovered stretch confirm that nitrile examination gloves have attractive handling characteristics that make them an acceptable alternative to latex examination gloves. While these laboratory studies confirm the superiority of nitrile examination gloves,
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clinical glove evaluation is still needed to determine their performance in the health care setting.
CONCLUSION The purpose of this study was to compare the biomechanical performance of powder-free, latex examination gloves with that of powder-free, nitrile examination gloves. Glove biomechanical performance was judged by standardized tests that measured glove thickness, glove puncture resistance, glove tape adhesion force, glove donning force, glove stiffness, and immediate unrecovered stretch. The examination gloves tested in this study included one powder-free, latex glove, one powder-free, nitrile glove, and another powder-free, nitrile glove that complied with NFPA 1999 Standards. The nitrile examination gloves tested in this study had almost twice the puncture resistance of the latex examination gloves. The powder-free N-Dex™ nitrile glove exhibited the lowest adherence of tape. Measurements of the handling characteristics of examination gloves using glove donning forces, glove stiffness, and immediate unrecovered stretch demonstrated that nitrile examination gloves are a suitable alternative to latex examination gloves. The glove donning forces for the nitrile and latex examination gloves did not differ significantly. Because these biomechanical studies indicate the superiority of the nitrile examination gloves, studies are now being undertaken that evaluate their performance in the clinical setting.
REFERENCES 1. Morbidity and Mortality Weekly Review. HIV epidemic and AIDS: trends in knowledge—United States, 1987 and 1988. MMWR 1989;38:353– 8,363. 2. Occupational Safety and Health Administration. Protecting Health Care Workers from Occupational Exposure to Bloodborne Pathogens, Title 29, Code of Federal Regulations, Part 1910.1030 (29 CFR 1910.1030). Washington, DC: U.S. Government Printing Office; 1992. 3. National Fire Protection Association. NFPA 1999, Standard on Protective Clothing for Emergency Medical Operations. Quincy, MA: National Fire Protection Association; 1997. 4. Woods JA, Lambert S, Platts-Mills TAE, Drake DB, Edlich RF. Natural rubber latex allergy: spectrum, diagnostic approach, and therapy. J Emerg Med 1997;15:71– 85. 5. Beezhold D, Beck WC. Surgical glove powders bind latex antigens. Arch Surg 1992;127:1354 –7. 6. Ruhl CM, Urbancic JH, Foresman PA, Cox MJ, Rodeheaver GT, Edlich RF. A new hazard of cornstarch, an absorbable dusting powder. J Emerg Med 1994;12:11–14. 7. American Society of Testing Materials. Test Method for the Analysis of Protein in Natural Rubber and Its Products, Vol. 9.02, ASTM D 5712. West Conshohocken, PA. 8. Jackson EM, Wenger MD, Neal JG, Thacker JG, Edlich RF. Inadequate standard for glove puncture resistance allows production of gloves with limited puncture resistance. J Emerg Med 1998;16:461–5. 9. Pavlovich LJ, Cox MJ, Rodeheaver GT, Edlich RF. Considerations in the selection of surgical gloves for tape wound closure. J Emerg Med 1994;13:349 –52. 10. Edlich RF, Kuphal JE. Bioengineering analysis of sutureless wound closure. Int Surg 1973;58:246 – 8. 11. Fisher MD, Neal JG, Kheir JN, Woods JA, Thacker JG, Edlich RF. Ease of donning commercially available powder-free surgical gloves. J Biomed Mater Res 1996;33:291–5. 12. Milton JS, Arnold JC. Introduction to probability and statistics, 2nd edn. New York: McGraw Hill; 1990.
PII S0736-4679(99)00133-X
Selected Topics: Wound Care
BIOMECHANICAL PERFORMANCE OF POWDER-FREE EXAMINATION GLOVES Mark D. Fisher, BA,* Vikram R. Reddy, BA,* Freddie M. Williams, BA, Kant Y Lin, John G. Thacker, PhD,† and Richard F. Edlich, MD, PhD*
MD,*
*Department of Plastic Surgery, University of Virginia School of Medicine and †Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia Reprint Address: Richard F. Edlich, MD, PhD, Department of Plastic Surgery, University of Virginia School of Medicine, Box 332, Charlottesville, VA 22908
e Abstract—Biomechanical performance studies were undertaken for powder-free, latex and nitrile examination gloves. Using standardized tests, examination glove performance was judged by measuring glove thickness, glove puncture force, glove tape adhesion force, glove donning force, glove stiffness, and immediate unrecovered stretch. Even though the nitrile examination gloves were thinner than the latex examination gloves, they exhibited a greater puncture resistance. In addition, tape adherence to the N-Dex™ nitrile glove was the lowest. Moreover, measurements of the handling characteristics of the nitrile examination gloves demonstrated that they are an acceptable alternative to latex examination gloves. While these biomechanical studies demonstrate the superiority of the nitrile examination gloves, clinical glove evaluation is still needed to determine their performance in the health care setting. © 1999 Elsevier Science Inc.
Disease Control and Prevention (1). The premise of universal precautions is that every specimen should be handled as if it came from someone infected with a blood-borne pathogen. All hospitals are mandated by the Occupational Safety and Health Administration (OSHA) to provide annual in-service training in, and to monitor compliance with, universal precautions to protect health care workers from blood-borne pathogens, including human immunodeficiency virus (HIV) and hepatitis B and C viruses. OSHA requires the employer to provide, at no cost to the employee, personal protective equipment, including gloves, to protect the employee against exposure to blood-borne pathogens (2). In addition, the National Fire Protection Association (NFPA) offers specific performance criteria involving glove exposure to surrogate virus challenge (3). Since the advent of universal precautions, latex gloves have been routinely used to protect health care workers against blood-borne pathogens. The frequency of latex glove usage increased dramatically, from 1 billion gloves in 1987 to 10 billion in 1996 (4). This dramatic increase in latex glove usage is associated with an increase in the frequency of latexallergic reactions in health care personnel that has reached epidemic proportions. The cornstarch powder on the surface of latex gloves has been shown to bind with the latex antigens and serve as a vector for this epidemic (5). In addition, the corn-
e Keywords—latex gloves; nitrile gloves; glove thickness; glove puncture resistance; glove stiffness; glove tape adherence; glove donning force; immediate unrecovered stretch
INTRODUCTION Health care workers in the Emergency Department (ED) as well as in prehospital treatment routinely wear examination gloves. This is consistent with the universal precautions instituted and recommended by the Centers for
Selected Topics: Wound Care is coordinated by Richard F. Edlich, MD, PhD, of the University of Virginia Medical Center, Charlottesville, Virginia
RECEIVED: 25 January 1999; FINAL ACCEPTED: 25 May 1999
SUBMISSION RECEIVED:
19 April 1999; 1011
1012
M. D. Fisher et al.
starch powder has been shown to be damaging to tissues (6). Consequently, many glove manufacturers are now manufacturing powder-free, latex-free synthetic examination gloves whose sizes correspond to the manufactured latex examination gloves. Because emergency medical personnel often do not know if their patients are sensitized to latex antigens, emergency health care workers are advised to wear latex-free, powder-free examination gloves. Some emergency medical personnel are now using these new powder-free, latex-free examination gloves in emergency medical systems throughout the country. These examination gloves are manufactured as nonsterile gloves designated for single-use only. The manufacturers provide the gloves in five sizes (extra small, small, medium, large, and extra large) and in ambidextrous sizing. To be labeled or otherwise represented as being compliant with NFPA 1999 standards, the gloves must meet or exceed all applicable requirements specified in this standard and be certified as such (3). Because many emergency medical personnel are still not familiar with these new powder-free, latex-free examination gloves, we undertook this study to compare the biomechanical performance of latex-free, powderfree examination gloves with that of a powder-free, latex examination glove. The performance of these different examination gloves was evaluated by standardized measurements that included the following parameters: thickness, puncture resistance, glove tape adhesion force, glove donning force, glove stiffness, and immediate unrecovered stretch.
MATERIALS AND METHODS Examination Gloves Three different commercially available powder-free examination gloves were evaluated in this study. The Best N-Dex® glove (Best Manufacturing Co., Menlo, GA) is a nitrile examination glove that is enclosed in a box with a label signifying that the glove complies with the NFPA 1999 Standard on Protective Clothing for Emergency Medical Operations (3). The Safeskin® nitrile examination glove (Safeskin Corp., San Diego, CA) is a powderfree nitrile glove. The Safeskin® PFE (powder-free examination) glove is made of powder-free latex. The gloves are packaged in a box with a label stating that the glove contains reduced levels of natural rubber latex proteins, containing 50 micrograms or less of total waterextractable protein per gm using the ASTM D 5712 Test (7). All three types of gloves tested were medium size, ambidextrous, and clean but not sterile.
Biomechanical Performance The biomechanical performance of the powder-free nitrile and latex gloves was determined by standard tests that measured glove thickness, glove puncture resistance, glove tape adhesion force, glove donning force, glove stiffness, and immediate unrecovered stretch.
Glove Thickness The thickness of each glove was measured using a spring-loaded micrometer. When measuring the thickness of the gloves, the spring-loaded micrometer and pad loaded the membrane with a compressive force of 14.6 kPa (2.1 lb/in (2). These measurements were made at the tip of the index finger for 10 different gloves of each brand. The data were reported as the average fingertip thickness for 10 different index glove fingertips.
Puncture Resistance The glove puncture resistance test was performed in accordance with American Society of Testing and Materials (ASTM) F 1342–91 (reapproved 1996) (8). This test has been incorporated as one of the standards of the NFPA 1999 Standards for Gloves. The test uses a metal puncture probe whose diameter is comparable to that of the end of a nail. Jackson et al. reported that the magnitude of the glove penetration forces for an 18-gauge hypodermic needle was significantly less than those for the metal penetrometer (8). Because our petition to the ASTM and NFPA to add the hypodermic needle test to the standard penetrometer probe test has not been approved by these organizations, we continued to employ the metal penetrometer probe test as the standard measure of glove puncture resistance in this study. A glove sample is placed in a stationary support assembly that is in turn affixed to the lower arm of a tension testing machine. A stainless steel pointed puncture probe is specially made to conform to set dimensions. This puncture probe is mounted to the penetrometer stand, and the whole assembly is attached to the compression cell of the Instron® Model 1222 (Instron Corp., Canton, MA). The puncture probe moves at a constant velocity until it punctures the material specimen. The force required to puncture the material specimen is measured by the compression cell. The testing machine is calibrated so that the error of the machine does not exceed 2% at any reading within its loading range. The specimen support assembly consists of two flat metal specimen support plates that clamp together. The
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Figure 1. The thickness of the nitrile examination gloves was significantly lower than that of the latex gloves.
sample specimen is held tightly between them, straining the glove specimen with a uniform movement of the pulling clamp. The two specimen support plates are connected to the testing machine using a machine interface plate. Each plate has 24 0.6 cm (1/4 in) diameter holes, located 1.9 cm (3/4 in) from the plate edge. Samples of the gloves are taken from the tip of the index finger and the specimen to be tested is placed in the support assembly. The reported puncture resistance is determined by the average of 10 tests. The two plates are marked and the holes are aligned before testing to avoid damaging the penetrometer and plates. The material support assembly is attached to the compression cell of the test apparatus and the puncture probe is positioned on the moveable arm of the Instron® tensile tester. The testing machine is set such that the penetrometer has a velocity of 50.8 cm/min (20 in/min) under load conditions and is uniform at all times. The penetrometer stops and retracts when it has punctured the sample specimen. The compression cell measures the maximum puncture resistance, and the results are recorded as the maximum puncture resistance in grams with a strip chart recorder and expressed in Newtons. If the sample specimen has not been penetrated, a maximum force of 23 kg (50 lb.) will be recorded. After each test is completed, the penetrometer is repositioned above each of the remaining guide holes and the test is repeated.
Glove Tape Adherence The adhesion of tape to surfaces is determined by peel adhesion (9). Peel adhesion is the force necessary to peel the tape from a surface, under standard conditions, at a specified rate and angle of pull (10). The tape used is a 6 mm ⫻ 10 cm Steri-Strip™ (3M Center, St. Paul, MN). Each tape sample is uniformly applied to the specified surface. The pressure of application is standardized by rolling a 1-kg weight across each tape. Peel adhesion measurements are made approximately 5 min after tape application. Each tape contained, for testing purposes, a 1/4 in tab that did not adhere to the specified surface. The level of adhesion is measured by clipping the exposed end of the tape to the Instron® Model 1123 tensile tester. The tape is then peeled from the specified surface at 100 mm/min, while measuring the force required to remove the tape.
Glove Donning Force One experiment was conducted to examine the forces required to don the three different brands of gloves with dry hands. A glove donning load tester was constructed consisting of a ring assembly with two tapered rings (diameter 125 mm) between which the cuff of the glove was secured (11). This ring assembly was attached to a rigid base that was set upon a calibrated scale. Each
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Figure 2. The puncture resistance of the nitrile examination gloves was nearly twofold greater than that of the latex examination gloves.
Figure 3. The N-Dex™ nitrile examination gloves exhibited the lowest adherence of tape.
Examination Glove Performance
subject with appropriately sized medium hands inserted a hand into a medium glove, while the maximum force required to don the glove was reproducibly measured and recorded on a strip chart recorder. As the eight volunteers performed the trials, they were trained to achieve uniformity in donning angle and the time to don with minimal movement during insertion into the glove. First, each subject was asked to don each of the three brands of examination gloves with dry hands. After donning each glove, the subject’s hand was washed and then dried to remove any surface lubricant or detergent. The order in which the gloves were donned was randomly assigned.
Glove Stiffness Curves expressing the relationship of elongation to force for each of the gloves were produced by stretching samples with an Instron® Model 1123 tensile tester and recording the forces with a strip chart recorder in gm and expressed in Newtons. Sample strips 2.5 cm wide were cut from the tubular area of the gloves close to the cuff. The strips were then pneumatically clamped into the moving cross-arm and load cell clamps of the Instron® tester. The gauge length, the distance between the two clamps of the sample, was 10 cm. The cross-arm speed was 5 cm/min, and the strips were stretched 2.5 cm. The forces required to stretch each of the samples 2.5 cm were used to calculate glove stiffness values for the three gloves. Stiffness was calculated by multiplying the stretch force by the length of stretch.
Immediate Unrecovered Stretch Recovery is the degree to which the glove samples were able to return to their original length after being stretched. To determine the recovery of the different gloves, each glove sample was first stretched 2.5 cm, after which tension was allowed to return to zero. The load and extension were graphically displayed. Data were collected from the graphically plotted data to calculate total change in sample length immediately after being stretched. The immediate unrecovered stretch was measured as the difference between the initial upload asymptote intercept and the initial download asymptote intercept at zero load and expressed in millimeters.
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Statistical Analysis of Data These data were first analyzed by using an ANOVA method to assess the statistical significance of each biomechanical parameter (12). A statistically significant difference in these measurements was confirmed (p ⬍ 0.05). A Duncan’s test was then used to statistically separate the gloves into groups.
RESULTS The Safeskin娂 latex gloves were thicker than the nitrile gloves (p ⬍ 0.05) (Figure 1). In contrast, the N-Dex娂 glove was significantly thicker than the other nitrile glove (p ⬍ 0.05). An analysis of variance confirmed that there were significantly different puncture resistant forces for the three examination gloves (p ⬍ 0.05) (Figure 2). The puncture resistance of the nitrile gloves was more than twofold greater than that of the latex gloves (p ⬍ 0.05). The puncture resistance of the nitrile gloves did not differ significantly. It is important to emphasize that the puncture resistances of the two nitrile gloves comply with the NFPA Puncture Resistance Standard of 4.45 N (3). The peel adhesion of microporous tape to the NDex娂 nitrile gloves was significantly lower than that encountered with any other examination glove (p ⬍ 0.05) (Figure 3). The peel adhesion to the Safeskin娂 Latex and Safeskin娂 nitrile gloves was nearly twofold and fivefold greater, respectively, than that found with the N-Dex娂 nitrile gloves. The glove handling characteristics were judged by the following parameters: glove donning forces, glove stiffness, and immediate unrecovered stretch. The glove donning force encountered with the latex examination gloves was the lowest but did not differ significantly from those found with the nitrile gloves (Figure 4). It is important to emphasize that all the gloves could be donned without tearing the glove. The stiffness of the Safeskin娂 nitrile gloves was significantly greater than that of any other examination glove (p ⬍ 0.05) (Figure 5). The stiffness of the N-Dex™ nitrile gloves did not differ significantly from that of the latex glove. There were noticeable differences among the gloves in terms of immediate unrecovered stretch, or length of change of sample after being stretched 2.5 cm (Figure 6). The glove sample with the least change in length after being stretched and returned to zero tension was the Safeskin娂 latex glove (p ⬍ 0.05). The N-Dex娂 nitrile glove had the second lowest value for immediate unrecovered stretch, followed by the Safeskin娂 nitrile glove.
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Figure 4. The glove donning forces for the examination gloves did not differ significantly.
Figure 5. The stiffness of the latex and N-Dex™ nitrile examination gloves were the lowest.
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Figure 6. The latex examination gloves had the lowest immediate unrecovered stretch.
DISCUSSION It is important to emphasize that the N-Dex娂 nitrile glove is the only examination glove tested that is certified to comply with NFPA 1999 Standards on gloves for emergency medical operations (3). Gloves in boxes labeled NFPA compliant meet the emergency medical glove requirements established by the NFPA 1999. All sample gloves are tested for watertight integrity and must have an acceptable quality limit of 1.5% leakage or better. Glove material samples shall exhibit no penetration of Phi-X-174 bacteriophage for at least 1 h. In addition, glove material samples are tested for ultimate elongation following heat aging and isopropanol immersion. The N- Dex™ nitrile glove, as well as the other nitrile glove which is not certified by NFPA 1999 Standards, have some unique advantages over latex gloves. Their resistance to puncture is more than twofold greater than that encountered with the latex gloves. In addition, the nitrile gloves are thinner than the latex gloves. There was one notable advantage of the N-Dex™ nitrile glove over that of the Safeskin™ nitrile glove: The adhesion of tape to the Safeskin™ nitrile glove was fivefold greater than to the N-Dex™ nitrile glove. Tape adherence to gloves is an extremely important consideration when emergency medical personnel use adhesive tape for securing bandages, i.v. lines, and tubes. An understanding of the handling characteristics of
examination gloves can be especially challenging because they are manufactured as ambidextrous gloves in only five sizes. Consequently, they are not designed to be form-fitted, like surgical gloves manufactured in half sizes from 5 to 9. Measurement of the glove donning forces demonstrated that all latex and nitrile examination gloves can be donned without tearing. The glove donning forces for the latex gloves are lower than those for the nitrile gloves, but do not differ significantly. The stiffness of the N-Dex™ nitrile gloves is remarkably similar to that of the latex gloves. The stiffness of the Safeskin™ nitrile glove is significantly greater than that of the other examination gloves. The immediate unrecovered stretch for the latex gloves is lower than those of the nitrile gloves. After the latex gloves were stretched and tension removed from the gloves, the latex gloves returned to their original dimensions. In contrast, the nitrile gloves elongated after stretching once the tension was reduced to zero. These measurements are consistent with the clinical observation that nitrile gloves will comfortably elongate over the wearer’s hands. In contrast, latex gloves resist elongation, applying continuous pressure to the wearer’s hands. These biomechanical measurements of glove donning forces, glove stiffness, and immediate unrecovered stretch confirm that nitrile examination gloves have attractive handling characteristics that make them an acceptable alternative to latex examination gloves. While these laboratory studies confirm the superiority of nitrile examination gloves,
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clinical glove evaluation is still needed to determine their performance in the health care setting.
CONCLUSION The purpose of this study was to compare the biomechanical performance of powder-free, latex examination gloves with that of powder-free, nitrile examination gloves. Glove biomechanical performance was judged by standardized tests that measured glove thickness, glove puncture resistance, glove tape adhesion force, glove donning force, glove stiffness, and immediate unrecovered stretch. The examination gloves tested in this study included one powder-free, latex glove, one powder-free, nitrile glove, and another powder-free, nitrile glove that complied with NFPA 1999 Standards. The nitrile examination gloves tested in this study had almost twice the puncture resistance of the latex examination gloves. The powder-free N-Dex™ nitrile glove exhibited the lowest adherence of tape. Measurements of the handling characteristics of examination gloves using glove donning forces, glove stiffness, and immediate unrecovered stretch demonstrated that nitrile examination gloves are a suitable alternative to latex examination gloves. The glove donning forces for the nitrile and latex examination gloves did not differ significantly. Because these biomechanical studies indicate the superiority of the nitrile examination gloves, studies are now being undertaken that evaluate their performance in the clinical setting.
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