Outdoor leisure activities or work in cold temperatures expose humans to cold stress. In this article, ‘cold work’ is used to define work in ambient temperatures lower than +10°C. Freezer rooms and food processing factories are examples of cold indoor workplaces. While open-pit miners, construction workers, mast and pole workers, and maintenance workers work long hours outdoors during cold seasons. Typically, hands are vulnerable to cooling while doing light physical work in the cold. Manual performance and dexterity are essential for workers to be able to perform their required work tasks (Figure 1).
Hands are First to Cool
If the body’s own heat production is not enough to maintain thermal balance, the body becomes cold. Vasoconstriction reduces blood flow to the skin and extremities, causing hands and fingers in particular to start to cool. Working bare-handed or with direct hand contact on cold surfaces may result in injuries such as frostbite. The cooling of fingers and hands is uncomfortable and markedly impairs manual performance and increases the possibility of mistakes and accidents.
Three types of hand cooling can be identified:
1. Convective cooling, where the hand is exposed to cold air
2. Conductive cooling, where the hand and/or finger is in contact with a cold surface while touching or gripping
3. Radiation through heat emission to a cold object
“choosing professionally tested cold protective gloves reduces the risk of these cooling effects”
However, mittens cause a large loss of dexterity in comparison to gloves. Heat loss from a gloved hand is greatest from the thumb and little finger. Therefore, these areas require more insulation than other parts. The fit, contact with cold surfaces or the materials of the glove, and wind, will considerably modify the local heat loss.
Dexterity with Gloves
Gloves alone, despite the ambient temperature, impair dexterity. Tactile sensation is impaired due to the use of gloves and tactual performance is also decreased, especially by the wrong size of glove. Clearly, glove thickness modifies the cutaneous sensation. Moreover, the thickness of a glove plays an essential role in the degree of finger dexterity loss. Even thin gloves can decrease finger dexterity by 60% compared to the performance of bare hands in the cold.
“even thin gloves can decrease finger dexterity by 60% compared to bare hands in the cold”
Maximal grip force of the hand reduces when gloves are worn compared to bare hands, and a thicker glove causes greater strength reduction. Better-fitting gloves result in better transmission of muscular force to grip force. Even a task which involves opening the hand to create an aperture requires a substantial effort of the muscles of the forearm when thick gloves are used.
Technology for Added Warmth
Technology and other applications can be added into a glove to create additional warmth. There are different auxiliary heating systems available, for example, liquid-filled heat packs and electrical heating. Additional heating can significantly increase skin temperatures on the fingers and maintain or alleviate reduction of dexterity.
The warming of the wrist/palm area has been shown to increase finger temperatures and blood flow in distal parts of the hand. Direct heating (even 42°C), applied to the forearm and face, reduced the decline in fine and gross manual dexterity by 20-50% at 0°C. Nevertheless, the finger temperature on the bare hand decreased to 11.6°C. Without any heating, the skin temperature on the finger was 10.9°C.
A power input of external heating is suggested to be at least 0.5 W per finger or 8-10 W per glove. This heating power, in addition to leather and woollen gloves, is shown to be sufficient in keeping fingertip temperature higher than 10°C in an ambient temperature of 0°C. However, there may be limitations from using external heating due to battery weight or power supply requirements.
Gloves in Cold Climates
Protective gloves can become stiff and brittle in very cold conditions. Low ambient or contact temperature has shown to change the mechanical properties of materials when they reached close to their glass transition temperature. Above the transition temperature, polymer materials are rather flexible, however, materials below the temperature become stiff and brittle. For example, the rate of crystallisation of natural rubber and neoprene reach their maximum at -25°C and -10°C, respectively. Temperature limits without leather cracking are defined as being close to -180°C. However, leather materials experience increased stiffness when temperatures decrease from 0°C to -20°C.
Cold Glove Standards
European Standards aim to create a common basis for requirements and test methods for protective gloves against cold, especially for manufacturers, as well as test institutes and end-users in Europe. The measured properties and their subsequent classification are intended to ensure an adequate protection level under different user conditions.
The following standards are normative for protective gloves against cold:
- EN 511 Protective gloves against cold (2006) – The standard for cold protective gloves specifies requirements and test methods for gloves which protect against convective and conductive cold down to -50°C. The pictogram of cold protective gloves is shown in Figure 2.
- EN ISO 21420 Protective gloves – General requirements and test methods (2020) – The standard determines requirements, e.g. for ergonomics, sizing, construction, visibility, maintenance, or comfort of the protective gloves. This standard is not used alone but only in combination with the appropriate specific standard(s).
- EN 388 (2016) + A1 (2018) Protective gloves against mechanical risks – This standard specifies requirements, test methods, marking and information to be supplied for protective gloves against the mechanical risks of abrasion, blade cut, tear, puncture and (if applicable) impact.
- EN ISO 7854 Rubber – or plastics-coated fabrics – Determination of resistance to damage by flexing (1997) – Describes the methods for the assessment of the resistance of coated fabrics to damage by repeated flexing.
In addition, standard ISO 13732-3: 2005 (Ergonomics of the thermal environment – Methods for the assessment of human responses to contact with surfaces – Part 3: Cold surfaces) outlines the safe time limits of bare hand/finger contact with various cold surfaces.
Performance Levels for Use
Performance levels against convective and contact cold are defined for cold protective gloves (Table 1). In addition, requirements and test methods, flexibility behaviour, water permeability and extreme cold resistance are given in EN 511 (2006). The minimum performance level must be 1 for convective and contact cold.
The standard 511 (2006) is given an informative annex to assist in the selection of cold protective performance levels. The annex shows the required thermal insulation level for three physical activity levels as a function of ambient air temperature at a wind speed below 0.5 m/s. Relevant parameters in the selection process that should be taken into account are environment (ambient temperature, wind speed, relative humidity), individual conditions (health and well-being, effect of other personal protective equipment by the person) and occupation (exposure time, physical activity, dexterity requirements, contact with cold items, contact with wet or dry objects).
Testing Cold Protective Gloves
Personal protective equipment (PPE) sold within the EEA must be CE marked and must meet the requirements of the PPE Regulation 2016/425 (or until 20.4.2019 the requirements of the PPE Directive 89/686/EEC). Manufacturers and distributors must have the products that are to be sold on EEA markets tested in an accredited laboratory and have the type examined to determine if they belong to Category II or III of the PPE Regulation. The manufacturer must also draw up an EC declaration of conformity for all PPE. Examined and accepted PPE can be recognised from its CE marking and each product’s own standard number.
The thermal insulation of gloves is measured by using a full-scale hand thermal model (Figure 3) in controlled climatic conditions (ambient temperature, wind speed and relative humidity). The surface temperature of the full-scale hand model will be in the range of 30-35°C, the ambient temperature being at least 20°C lower, wind speed 4 m/s and relative humidity 50%. The final result is a mean value of two independent measurements.
Thermal resistance of glove fabrics, fabric assemblies or fibre aggregates is measured under a pressure of 6.9 kPa by using the thermal resistance testing equipment (Figure 4). The material is placed between hot and cold plates. The result is a mean value of two independent measurements and is expressed as m2K/W.
Research to Prevent Hand Cooling
Despite climate warming, northern areas will remain cold from a human point of view. Thermoneutral temperature (causing no heat or cold stress) for a minimally clothed person at rest is as high as 27°C and during maximal exercise is circa 11°C. Cold and harsh environments are a challenge for the workers, especially cold protection of hands in correlation to hand performance and dexterity. Cold and rapidly changing weather conditions cause challenges for the workers, and especially workers with circulatory disorders.
The following are two recent research cases that studied hand cooling and cooling prevention in outdoor and indoor cold conditions in northern areas.
The “SmartPro” Project
The “SmartPro” research project was created to study hand cooling and develop solutions to individually protect the hands in outdoor cold work in northern areas. It also aimed to find different cooling patterns of the hands and fingers and create interactive heating systems using existing technology.
Hand and finger skin temperatures were measured while ten test subjects were standing still for an hour in an ambient temperature of -10°C. The subjects wore gloves and appropriate winter clothing to prevent whole body cooling. In the study, three different cooling patterns of fingers, without additional heat, were observed.
1. a rapid cooling group
2. a slow cooling group
3. a cold tolerant group
Prototypes of heated gloves were produced by integrating electrically heated carbon tape into gloves. The effectiveness of the heating elements and their optimum placement on the hand was studied. The heating was adjusted to maintain the temperature between 26-28°C. Finger dexterity with gloves was also tested by the Lafayette Hand Tool Dexterity test, Minnesota Pegboard and the dexterity test according to standard EN 420+A1 (2009). The additional heating power required with gloves (thermal insulation was 0.191-0.224 m²K/W) to maintain the skin temperature of the hand in thermoneutral at temperatures of +10°C, 0°C, and -10°C and in wind speeds of 0.3 m/s and 4 m/s were measured by the thermal hand model.
The results showed that the additional heating required for work gloves was about 9 W per hand in calm wind and about 12 W per hand in moderate wind (4 m/s) at an ambient temperature of -10°C to prevent hand cooling. The finger dexterity with gloves was dependent on the material structure, its flexibility, and patterning of the glove and fingertips.
The heating solution was shown to be the most suitable for subjects that have fast or moderately cooling fingers. Figure 5 illustrates the development concept in the SmartPro project that can be used to evaluate workers’ individual sensitivity to cold, together with occupational health care personnel.
This project was carried out in co-operation with the FIOH and SINTEF research institute from Norway. The project was part of the Saf€ra programme and the work of the FIOH was financially supported by the Finnish Work Environment Fund.
Dexterity in Food Processing
The ambient temperature in the food processing industry varies generally between 4°C and 6°C, and products are often frozen or cooled below 4°C. According to a questionnaire compiled at a food processing company, 90% of the workers complained of cold hands. Most often the reason was from the contact with frozen products while handling them. In these industries, cotton under gloves are used for cold protection and the thin plastic gloves for hygiene reasons. One third of the responses reported a wetting of the cotton or incision gloves under the plastic gloves, and 40% of responses stated that the provided gloves did not protect against cold. Measured finger temperatures were as low as 10°C while workers were cutting cold meat products. Finger temperatures below 13-15°C are known to impair finger dexterity. Meat cutting with knives and scissors requires precise manual dexterity to work with a rapidly moving conveyor belt (Figure 6). Therefore, the protective gloves cannot be too thick. The workers complained that their incision gloves were often too thick to reach the optimal finger dexterity.
Hygiene regulations require high washing temperature which further restrict the choice of suitable glove materials. Slight changes in glove material are not enough to solve the problem of hands and fingers cooling. Tackling the combination of cold environments, handling cooled or frozen products, the hygiene requirements of the protective glove materials, and overall finger dexterity is a challenging task. Smart textile materials or other smart solutions for gloves could be a future solution for the current cold work problem in the food processing industry. This study was performed by FIOH in co-operation with HKScan Corporation and was financed by
the Finnish Work Environment Fund and HKScan.
The Finnish Institute of Occupational Health (FIOH) is an expert multidisciplinary research and training organisation that promotes the occupational health and safety of the working population, and enhances well-being through work.
FIOH has special laboratories for testing protective clothing, fabrics and gloves against cold and survival, and diving suits used in cold water. The testing laboratory is accredited according to EN ISO/IEC 17025 (T013) by FINAS (Finnish Accreditation Service).
Kirsi Jussila, DSc (Tech), is a Specialist Research Scientist at FIOH. Her research is focused on clothing; physiological properties of cold protective clothing; gloves, headwear and shoes; and functionality and usability of protective clothing and garments; and their compatibility and effects on user’s comfort and performance. ORCID ID: 0000-0003-1767-9745.
Sirkka Rissanen, PhD, is a Senior Research Scientist at FIOH. Her research is focused on human thermoregulation and manual performance in cold temperatures. ORCID ID: 0000-0002-5864-2028.