¹ Center for Mechanical & Environmental Systems Technology (CMEST), University of Nevada, Las
   Vegas, Nevada, USA
² Occupational Medical Consultants, 6515 Barrie Road, Edin, Minnesota, USA

INTRODUCTION

Repetitive trauma associated with excessive vibration directed into the hands and arms is a significant health problem in U.S. industry. It is estimated that between two to four million workers are exposed to on-the-job hand-arm vibration in the U.S. and that around 50% of these workers either have or will develop symptoms associated with hand-arm vibration syndrome (HAVS). HAVS is associated with the destruction of the small blood vessels and with nerve damage in the fingers. HAVS is caused by excessive vibration directed into the hands from vibrating hand tools and vibration-intensive work processes. Symptoms associated with HAVS usually show up as a combination of finger blanching, particularly in response to cold, and progressive finger numbness.⁽¹⁾ In advanced stages, HAVS can result in the loss of tactile discrimination and manipulative dexterity.⁽¹⁾ When the level of vibration exposure to the hands is excessively high, symptoms associated with HAVS can appear within as little as one year’s time.⁽²⁾

While most emphasis in the area of hand-arm vibration has been placed on HAVS, NISOH publication 97-141 indicates there is evidence of a relationship between the use of vibrating tools and carpal tunnel syndrome.⁽³⁾ The pathology of the mechanisms of the onset of carpal tunnel syndrome is still uncertain as to whether it is directly related to the ergonomics of hand position or gripping associated with the use vibrating hand tools. However, this relationship is becoming increasingly important in dealing with hand-related injuries associated with the use of vibrating tools.

One method of reducing vibration energy into the hand and arm is to use protective clothing, in particular antivibration gloves. NIOSH publication 89-106 states that strategies for reducing hand-arm vibration in the U.S. shall be supplemented by the "use of antivibration clothing, mittens, gloves, and equipment."⁽⁴⁾ The NIOSH publication further states that the vibration-damping material in an antivibration glove must:

• "provide adequate damping with minimal thickness so that the dexterity required for safe and efficient tool operation will not be reduced, and

• have adequate damping characteristics over the vibration frequency spectrum associated with HAVS."

The International Organization for Standardization adopted ISO Standard 10819 to define the performance criteria and related test procedures that must be met and used to classify a glove as an antivibration glove.⁽⁵⁾ An antivibration glove must:

• have an average ISO weighted transmissibility of less than 1, TR_M < 1, in the mid frequency range from 16-400 Hz and of less than 0.6, TR_H < 0.6, in the high frequency range from 100-1,600 Hz;

• be a full-fingered glove that has the same vibration protection in the palm and fingers.

Many glove manufactures make and market gloves that are advertised to reduce vibration into the hand and arm. However, many of these gloves are ineffective in reducing vibration, and nearly all of them do not meet the requirements of ISO Standard 10819 to be classified as an antivibration glove. Thin flexible air bladders have been developed that can be used as vibration-damping elements in gloves. The air bladders are effective in reducing vibration energy into the hand and arm. Tests have shown that a glove that uses an air bladder as its vibration-damping element will meet the requirements of ISO Standard 10819 to be classified as an antivibration glove.

ERGONOMIC REQUIREMENTS FOR ANTIVIBRATION GLOVE DESIGN

The ergonomic effects of a tool on the hand include hand posture, grip strength, push force, tactile feedback, and temperature. The design of an antivibration glove must address these issues. Five ergonomic factors must be considered in the design of an antivibration glove. Paying proper attention to these factors increases the effectiveness of the glove in reducing vibration while making the glove comfortable to wear.

• The thickness of the vibration-damping material placed in a glove to reduce vibration must be relatively thin. Placing vibration-damping material in the palm and the finger and thumb stalls of a glove increases the effective diameter of a tool handle when clasped while wearing the glove. Placing a material with too great a thickness in a glove can make the glove feel bulky and uncomfortable when clasping a hand tool or work piece. This can also make proper control of a tool difficult to maintain. A larger diameter handle requires a greater grip force to clasp the handle with the same grip effort, as compared to a smaller diameter handle. This increases muscle fatigue and the intracompartment pressure in the carpal tunnel in the wrist.⁽⁶⁾ Increased muscle fatigue and intracompartment pressure in the carpal tunnel raises the risk of developing carpal tunnel syndrome.⁽⁷⁾ Both HAVS and carpal tunnel syndrome must be considered when designing an antivibration glove. Increasing the thickness of the vibration-damping material in a glove usually increases the effectiveness of the glove in reducing vibration. However, thicker material can cause a glove to feel bulky and be uncomfortable. It can also increase the risk of developing carpal tunnel syndrome when using the glove over an extended time period. Material placed in the finger and thumb stalls of a glove should have a thickness less than 4.6 mm (0.18 in.) and in the palm area less than 6.4 mm (0.25 in.).

• Vibration-damping materials placed in a glove should be flexible and pliable, and they should not interfere with tactile feedback. These materials should easily conform to the natural flex-lines in the palm and fingers. This allows the worker to easily maintain control of his tool or work piece. Vibration-damping materials should minimize the reduction in tactile feedback associated with their use. To properly perform work operations, an operator must be able to feel his tool and/or work piece.

• The vibration-damping material must cover the full palm area and all of the digits of the fingers and thumb. Vibration from a tool or work piece enters the hand at the palm, fingers and thumb. The primary damage associated with HAVS occurs in the fingers and thumb. Thus, to protect the fingers and thumb, all of the digits of the fingers and thumb must be isolated from the tool or work piece. Figure 1 shows a schematic drawing of an air bladder between a handle and the hand.

Figure 1 Air Bladder between the HandleAnd Hand

• An antivibration glove must have an opposed thumb. Figure 2 shows a glove with a wing thumb. A wing thumb is often used in a glove because it simplifies the manufacturing of the glove. When a glove that contains vibration-damping material and that has a wing thumb is used to clasp a tool handle, the material in the thumb stall rotates to the outside surface of the thumb. This places the thumb in direct contact with the tool handle, exposing it to vibration. Using an opposed thumb, as shown in Figure 3, will prevent this. When a glove with an opposed thumb is used to clasp a tool handle, the vibration-damping material always stays properly positioned between the thumb and handle.

Figure 2 Glove with a Wing Thumb

Figure 3 Glove with an Opposed Thumb

• An antivibration glove should be loose fitting. Vibration-damping material that is placed in an antivibration glove can make the glove feel tight and stiff, particularly in the finger and thumb stalls. This usually reduces manipulative dexterity. Over-sizing a glove to accommodate vibration-damping material will increase manipulative dexterity. It is particularly important to over-size the finger and thumb stalls.

GLOVE WITH AN AIR BLADDER VIBRATION-DAMPING ELEMENT

A thin layer of air placed between a vibrating handle or work piece and the hand is the most efficient means of attenuating vibration into the hand. A thin layer of air can be achieved with an air bladder that is made by welding two layers of thin-film thermoplastic material together with a quilted pattern of weld points and with weld lines that correspond to the natural flex-lines of the hand. An air bladder made by this process is thin, pliable, and flexible. This allows the bladder to naturally conform to the palm and fingers when clasping a handle or work piece. The air bladder for each hand has a bulb inflater. The inflater is connected to the air bladder by means of a flexible tube that allows the inflater to be placed on the backside of the glove. Figure 4 shows a picture of an air bladder placed on the outside of a glove. The air bladder is placed in a pocket in the glove between the palm of the hand, fingers and thumb and the outside shell of the glove. A thin cotton or Lycra material is placed between the air bladder and the hand to prevent the hand from sweating. The outside shell of the glove can be leather, Kevlar, or any other durable material.

Figure 4 Air Bladder Placed on the Palm and Fingers of a Glove

TEST RESULTS ASSOCIATED WITH GLOVE VIBRATION-DAMPING MATERIALS

Table 1 shows the ISO weighted and linear vibration transmissibility values of gloves that contain vibration-damping materials commonly used to reduce vibration. Lower transmissibility values indicate greater effectiveness in reducing vibration. Figure 5 shows the vibration transmissibility values of the gloves in Table 1 as a function of third octave center frequencies. Table 1 and Figure 5 indicate that a glove with an air bladder had the best performance. It is the only glove that was tested that met the requirements of ISO Standard 10819 for classification as an antivibration glove. A glove with an air bladder was tested at the three laboratories listed in Table 2. It met the requirements of ISO Standard 10819 for classification as an antivibration glove at all three laboratories.

Figure 5 Third Octave Transmissibility Values of Selected Glove Materials

Gloves made with viscoelastic materials, such as Gelfom, Sorbothane, Viscolas, and Akton require a significantly thicker layer of the indicated material in the palm and fingers to provide vibration protection equal to that achieved with an air bladder. Gloves that use these materials are generally stiff and/or bulky. These materials, when used in a thick configuration in a glove, result in increased muscle fatigue and intracompartment pressure in the carpal tunnel. These increase worker fatigue and reduce tactile feedback. When the vibration-damping material in a glove is too thick, the risk of developing carpal tunnel syndrome with prolong use is increased.

SUMMARY AND CONCLUSIONS

A glove made with an air bladder vibration-damping element met all of the NIOSH, ISO, and ergonomic design requirements for a properly designed antivibration glove.

• It met the requirements of ISO Standard 10819 to be classified as an antivibration glove.

• It significantly reduced the vibration into the hand.

• It was thin, pliable and flexible.

• It naturally conformed to the flex-lines in the palm and fingers.

• It was comfortable to wear.

• It allowed the worker to maintain control of his tool or work piece.

• It allowed the worker to feel what he was doing.

• It was readily accepted by workers who used it.

The latency period for HAVS is the time it takes for the first symptoms of HAVS to appear. The latency period is determined by many factors. However, the most significant factor is the amplitudes of the vibration energy into the hands or the vibration exposure. Gloves with air bladder vibration-damping elements have proven themselves to be effective in reducing vibration exposure. From a research perspective, decreasing the vibration into the hands increases the latency period associated with the onset of HAVS symptoms.

When applied to gloves, air bladder technology lends itself nicely to various glove styles and applications. These styles, along with the flexibility, manipulative dexterity, and comfort associated with gloves made with an air bladder, have led to good worker acceptance of these gloves.

Air bladder technology, when used in gloves, provides credible personal protection for workers exposed to hand-arm vibration. It remains to be seen whether or not industry will utilize this technology to decrease the number of work-related hand injuries associated with exposure to hand-arm vibration. Whatever happens, it is time for the community that has extensively studied and defined disorders associated with hand-arm vibration to shift from recognition, analysis, and quantification of these disorders to intervention and prevention of work-related injuries associated with hand-arm vibration.

REFERENCES

1. Pelmer, P. L., Taylor, W., and Wasserman, D. E., Hand-Arm Vibration, A Comprehensive Guide for Occupational Health Professionals, 1992, Van Nostrand Reinhold.

2. ISO Standard 5349: Mechanical vibration - Guidelines for the measurement and the assessment of human exposure to hand-transmitted vibration, 1986, International Organization for Standardization, Geneva, Switzerland.

3. NIOSH Report: MUSCULOSKELETAL DISORDERS (MSDS) AND WORK PLACE FACTORS – A critical Review of Epidemiologic Evidence for Work Related Musculoskeletal Disorders of the Neck, Upper Extremity, and Low Back, 1997, DHHS (NIOSH) Publication No. 97-141, National Institute for Occupational Safety and Health, 4676, Columbia Parkway, Cincinnati, Ohio, USA.

4. NIOSH Criteria for a Recommended Standard: Occupational Exposure to Hand-Arm Vibration, 1989, DHHS (NIOSH) Publication No. 89-106, National Institute for Occupational Safety and Health, 4676, Columbia Parkway, Cincinnati, Ohio, USA.

5. ISO Standard 10819: Mechanical vibration and shock - Hand-arm vibration - Method for t he measurement and evaluation of the vibration transmissibility of gloves at the palm of the hand, 1996, International Organization for Standardization, Geneva, Switzerland.

6. Radwin, R. G., Armstrong, T. J., and Chaffin, D. B., Power Hand Tool Vibration Effects on Grip Exertions, 1987, Ergonomics, 30(5), 833-855.

7. Szabo, R. M. and Chidgey, L. K., Stress Carpal Tunnel Pressure in Patients with Carpal Tunnel Syndrome Normal Patients, 1989, Journal of Hand Surgery, 14A, 624-627.

ACKNOWLEDGMENTS

The authors wish to express their appreciation to ErgoAir, Impacto Protective Products, and Dielectrics Industries for their assistance and support in the research reported in this paper. The air bladder technology reported in this paper is the proprietary property of ErgoAir, Inc. and is protected by US Patents 5,144,708, 5,372,487, 5,537,688, and 5,771,490. Other US and international patents are pending.

Paper presented at:
8th International Conference on Hand-Arm Vibration
Umea, Sweden
June 9-12,1998