1. Introduction
Human hands have a rather complex anatomical structure and are the main limbs in performing occupational and non-occupational activities. The physical and tactile capabilities of hands enable us to perform a variety of tasks and motions such as delicate and fast manipulations, power gripping, force exertion, and repetitive motions with high accuracy [1,2]. Dexterity is a term used for explaining the ability of hands and fingers in manipulating objects with various shapes and sizes. Dexterity is mainly affected by the motion range of fingers, hand, forearm, and arm. It is also influenced by nerves, muscles, and tendons of hands and fingers [3,4]. Hand grip strength refers to the amount of force transmitted to an object when it is grasped by hand and fingers. Dexterity and hand grip strength are two main factors determining the ability of an individual in performing a wide range of manipulative tasks such as writing, holding hand tools, using screwdrivers for fastening a screw, using a wrench for unscrewing a bolt, using a hammer for driving a nail, using shovels for digging, and so on [[5], [6], [7], [8]].
As many occupational activities are performed by hand, occupational hand injuries are widespread [9,10]. Therefore, hands must be protected against a wide range of mechanical (abrasion, compression, cutting, fracture, puncture, and so on), thermal (cold and hot surfaces), radiation (ultraviolet, infrared, X, gamma, so on), chemical (corrosives, irritants, sensitizers, and so on), biological (infectious agents), and electrical hazards at workplaces [[11], [12], [13]]. Workers use various types of gloves to prevent their hands from being injured by these hazards [14]. There are many types of protective gloves available in the market designed to protect hands and fingers in various ways. It should be always taken into account that each type of safety glove is designed and made to provide protection against a particular set of hazards and it would not be effective in protecting hands against other hazards. The type of hazards, the tools to be used, duration of the task, and parts of hands, fingers, and forearm that need to be protected are important factors to be considered in designing, manufacturing, or selecting appropriate safety gloves [15]. Various materials are used in manufacturing protective gloves based on the type and degree of required protection. Leather, plastic, tarpaulin, nylon, and Kollar are some commonplace materials used in this regard. Some types of gloves may have an additional coating layer which is normally made of polyvinyl chloride, nitrile, and vinyl, while some others such as those used in butchery are strengthened using metal mesh to manage cutting forces. In addition to construction materials, glove thickness is another important design parameter. The glove thickness should be selected based on the required level of protection. For example, thicker electrical protective gloves are required when higher voltage is dealt with [16]. A main problem related to protective gloves is that they can negatively affect dexterity and hand grip strength, making it difficult for workers to perform their tasks while wearing gloves. In such a situation, some individuals may prefer to not wear their safety gloves, making their hands unprotected against occupational hazards and prone to injuries [15].
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Increase in the glove thickness and number of layers can negatively affect manual dexterity [4,17]. The flexibility of gloves is a function of both their thickness and construction materials. Inflexible gloves have a higher negative effect on dexterity, therefore a tradeoff between these two design parameters should be taken into account [17]. Gloves can negatively affect grip strength. Most previous studies demonstrated that wearing any type of gloves has a negative effect on grip strength, for example Wimer et al. [18], Ramadan [19], and Zhao et al. [20]. However, the reducing effect of wearing gloves on grip strength is not supported by all studies. In the other words, there are some studies reporting contradictory results. In this regard Shih et al. [21] demonstrated that wearing multilayer latex gloves could even increase grip strength or Hamouda et al. [22] reported that anti-vibration leather gloves do not affect grip strength significantly. Therefore, the negative effect of gloves on grip strength is a function of its design and can be reduced to a minimum possible value. Manufacturers should design and manufacture gloves with the least possible negative effect on all hand performance indicators, particularly grip strength and dexterity. Construction materials, glove thickness, and gloves fitting are some important design parameters affecting dexterity and hand grip strength [18].
There are several tools and techniques available for measuring dexterity and hand grip strength of hands while wearing gloves. Purdue Pegboard test, O’Connor Dexterity test, and Bennett hand tool dexterity test are some well-known dexterity tests. These tests are also very useful in assessing gloves design. However, it should be noted that a particular type of dexterity test is not appropriate for all purposes. Some of these tests make attempts at simulating intricate hands and fingers motions, while some others are appropriate for less intricate movements of hands and fingers [4,6]. A question to be answered here is which test is appropriate for a particular purpose.
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Jamar dynamometer is the most commonly used tool in measuring hand tool strength [23]. However, in recent years other types of dynamometers were also developed, such as the squeeze (bulb) dynamometer. Previous studies have shown the excellent reliability of this tool in measuring hand grip strength [24]. Moreover, the bulb dynamometer is less painful and more comfortable to use than the Jamar dynamometer [25]. People with big hands may struggle to use conventional Jamar dynamometer, while there is no such a problem when the bulb dynamometer is used. Moreover, the bulb dynamometer is less expensive compared to the Jamar dynamometer [23,24]. So far, few studies have used this dynamometer for measuring hand power strength while wearing gloves. In this study, we used the bulb dynamometer instead of the traditional Jamar dynamometer to measure hand grip strength while various types of gloves are worn.
According to mentioned issues, all types of safety gloves are not equal in terms of their effects on dexterity and grip strength. Further, the available dexterity tests are different in terms of their ability to discriminate against various types of gloves. In other words, the discrimination power of dexterity tests is not the same. Moreover, to the best of our knowledge, no study has compared general safety gloves and firefighting gloves in respect to their effects on hand performance indicators. Consequently, the present study had several objectives: 1) to compare various types of safety gloves in terms of dexterity using various types of dexterity tests, 2) to compare various types of safety gloves in terms of hand grip strength measured by the bulb dynamometer, 3) to compare several types of dexterity tests in terms of their ability in discriminating safety gloves, 4) to assess the level of perceived comfort while wearing various types of safety gloves, and 5) to assess the effect of glove thickness on the hand dexterity and power grip strength. To the best of our knowledge, this study is the first on comparing firefighting gloves with general safety gloves.
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