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Handling Extreme Temperatures

Published: 07th Nov 2016

Many different types of gloves are available to protect hands and forearms from cuts, abrasions, puncture wounds, vibration, skin contact with hazardous chemicals and some electrical shocks. Other dangers to hands come from exposure to heat and/or flame and cold. SATRA has invested in technology to test the thermal resistance aspects of gloves and SATRA’s Hannah Althorpe provides an overview.

New European PPE Regulation (EU) 2016/425

In Europe, items worn or held to provide protection fall within the scope of the Personal Protective Equipment (PPE) Directive 89/686/EEC, soon to be replaced by the PPE Regulation (EU) 2016/425. Both the Directive and Regulation specify that the manufacturer is responsible for ensuring that the product meets a number of basic health and safety requirements. A process of type examination and approval must be followed using an EU Notified Body, such as SATRA, before products can be placed on the market.

As a part of this process product assessments and tests will be required to prove that the product meets the basic health and safety requirements. Many harmonised European standards have been developed to help standardise this process. They allow a presumption of conformity to the Directive that the Notified Body can use when assessing the product. This article discusses those harmonised standards relevant to gloves protecting against heat, flames and the cold.

EN 407: 2004

EN 407: 2004 – Protective gloves against thermal risks (heat and/or fire) is a general standard designed to be used for any glove which is to be produced and sold as providing protection against thermal hazards. The methods and performance levels included in the standard are dependent on the field of application of the glove. Some specialist applications are covered in additional standards such as EN 12477: 2001 - Protective Gloves for Welding.

EN 407:2004 includes six thermal tests; burning behaviour, contact heat, convective heat, radiant heat, and small and large splashes of molten metal. It also refers to EN 388: 2003 and EN 420: 2003+A1: 2009 for mechanical and general performance requirements. The test(s) selected are based on the intended use of the glove.

Burning behaviour

The burning behaviour test is undertaken in a controlled chamber where the glove is suspended vertically by the cuff so the middle finger is at the midpoint of the lower edge. The burner is then mounted at an angle of 30° to the vertical with a distance of 20mm from the tip of the middle finger of the glove to the burner. This is the point of application of the flame. Two gloves are tested, the first for three seconds of ignition time and the second for 15 seconds. The afterflame and afterglow times are recorded and the glove inspected for damage to the materials and any seams present.

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Contact heat

The contact heat test is designed to record the thermal resistance of a sample by measuring the rate of temperature rise across it.

The contact heat test involves placing samples of the palm of the glove onto a heated plate at different temperatures and recording how long it takes for the temperature on the other side of the samples to rise by 10°C. This is called the threshold time. A contact heat performance of level 3 can only be claimed if the burning behaviour performance is also level 3 or 4.

Convective heat

The convective heat test is similar to the burning behaviour test although a more aggressive flame is used and all the different components of the glove are tested; for example the cuff, back and palm. Samples of different components or layers of the glove are tested and the time taken for the temperature to rise by 24°C is assessed. A convective heat performance level can only be claimed if the burning behaviour performance level is 3 or above.

Radiant heat

The radiant heat test is used to test the back of the glove to ensure the materials can resist high levels of heat radiating through the glove to the hand to prevent injury. Samples are taken from a pair of gloves and are exposed to a heat flux density and again the time taken for the temperature to rise by 24°C is assessed to determine the performance level.

Small drops of molten metal

This test is designed to give the wearer some protection when working in close proximity to small amounts of molten metal, for example during welding operations. To test a glove’s performance level against small droplets of molten metal, four test samples are taken from a pair of gloves: two from the palm and two from the back of the hand. These samples are mounted in a chamber and subjected to droplets of molten metal, e.g. copper. The number of metal droplets required to raise the temperature by 40°C on the other side of the sample is recorded. The performance level is based on the mean values of either the palm samples or ‘back of the hand’ samples; whichever is the lower.

Large quantities of molten metal

The large molten metal test is carried out on three samples when testing for each performance level. The glove sample is placed over a PVC foil skin simulant and the required quantity of molten metal, for example iron, is poured over the sample. The skin-simulant is assessed after each test and should not show any signs of smoothness or changes in the grained surface. Failure also occurs if any droplets remain stuck to the sample or the sample ignites or is punctured.

General and mechanical performance

For all the standards discussed above, the physical characteristics of the glove also need to be assessed. The material of the protective gloves shall meet at least a performance level 1 for abrasion and tear resistance, tested in accordance with EN388: 2003, and all relevant requirement of EN420: 2003+A1: 2009. General requirements for both these standards are listed below.

EN511: 2006 –Protective gloves against cold

Wearers may encounter a number of hazards when working in a cold environment without adequate hand protection. When hands get cold, workers can experience a loss of sensation and impaired movement. It can be more difficult to handle small objects and suffer a decreased grip which can result in accidents from dropping objects or from applying too much pressure to compensate for the lack of grip. In extreme cases, exposure to cold environments without the right protection can lead to frostbite.

Heat loss from hands can occur through a number of processes. The main ones are ‘conduction’ – heat transfer when the glove is in contact with a cold object or something they are holding, and ‘convection’ – heat loss into the surrounding atmosphere, which is highly dependent on movement of the surrounding air.

There is a European standard referenced EN 511: 2006 to assess the performance of a glove’s protection for the hands against cold hazards which has several tests including convective cold, contact cold, water penetration and flexibility behaviour.

Convective cold

To determine the thermal insulation of a glove, the convective cold test is used to measure the power required to maintain a constant temperature between the surface of a heated hand model and the ambient atmosphere within a controlled chamber. The more electrical power required, the lower the thermal insulation value of the glove.

The convective cold test is a complex procedure requiring specialist equipment. The apparatus required for this test includes a computer-controlled heated hand (size 9) placed in an environmental chamber. In the chamber, the temperature is set to at least 20ºC below that of the heated hand, and there is a defined air velocity of 4 ± 0.5 m/s and relative humidity of 50 ± 5%. When the temperature of the hand and the power consumption are at a steady level, the measurements are taken of their average values for a period of 10 minutes.

Contact cold

The contact cold test involves the glove materials used for the palm side of the fingers of a glove being placed between metal plates which are set at different temperatures. The measured temperature drop across the test specimen is used to calculate its thermal resistance.

Flexibility behaviour and extreme cold flexibility test

For gloves to be usable at low temperatures they need to remain flexible. The standard contains two flexibility tests in order to assess this. The first is the flexibility behaviour test and this is only for coated materials where the assessment is looking for cracks that form in the glove’s coating during a 10,000 cycle low temperature flex test. The other test is the extreme cold flexibility test designed for gloves intended to be used in environments below -30ºC. This test involves bending samples on a special jig at -50ºC and assessing the sample for cracks.

Water penetration

Gloves are tested for integrity as a whole by a wearer immersing them in water up to the wrist line. Clenching movements are then made with the fingers for two minutes and then they are held stationary in the water for a further three minutes. The gloves are worn by a subject who checks at regular intervals for any leaks while flexing their hands and fingers. The glove reaches a performance level of 1 if no leaks are present. If the glove fails to meet this requirement, then the performance level will be 0 and a warning must be supplied by the manufacturer to inform users that the glove may lose its insulation properties when wet.

General and mechanical performance

As in EN407: 2004, the physical characteristics of gloves tested to EN511:2006 also need to be assessed, such as resistance to abrasion and tearing. These assessments are based on the EN 388: 2003 and EN 420:2003+A1: 2009 standards discussed below. The gloves must meet a performance level 1 of EN388: 2003 in abrasion and tear as a general requirement and this minimum level increases according to the different levels of protection against cold.

EN 420: 2003+A1: 2009

This standard is designed to ensure that the gloves themselves do not cause harm to the wearer and are comfortable to wear. Tests and requirements include the pH value and chrome VI content of leather (other chemical tests may be required as part of innocuousness testing), water vapour transmission and absorption of materials. Further procedures are called up for the sizing of the glove and its effect on finger dexterity. There are also general requirements for the information to be supplied with, and marked on, the glove. It should be noted that not all the performance tests in this standard are mandatory.

EN 388: 2003

This European standard (currently under revision and expected to be published later this year) is widely used in assessing gloves for general industrial applications. It is also referred to in many of the specialist glove standards such as those discussed above. It includes four main physical tests to assess the resistance of the glove’s palm area to mild abrasion, cutting, tearing and puncture. The performance of the glove is graded in accordance with four or five performance levels in each test.

Summary

While hand injuries still form a high percentage of accidents both at work and at home, many of them are easily preventable by wearing appropriate protective gloves. Increasing legislation and obligations for employers and manufacturers to provide improved safety equipment and adequate protection against hazards such as heat and/or flame and cold is leading to advances in material technology and better protective products. This is resulting in better designed and more comfortable gloves which, in turn, should lead to a reduction in injury statistics.

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Hannah Althorpe is a member of SATRA’s Safety Product Testing Team. She is involved in testing a range of PPE products including gloves, fall arrest products and sports equipment.
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