As much as you'd glove to think otherwise, hand protection is a complex field, and not every glove is suited for every purpose, particularly chemical-resistant gloves.

Within many industrial environments or applications, the risk of variable temperatures can be as important as the primary chemical hazard. Understanding how chemical gloves behave and interact with both contact heat and cold is an important factor to remain protected and productive.

How hand protection will perform under variable temperature conditions will depend on the rubber polymer it is made from. Heat and cold have varying effects on different types of rubbers which impact both protection and performance, and may present major concerns depending on the hazards present in your workplace.  

PVC Gloves

PVC gloves have a large proportion of plasticisers within them to make the raw PVC, which is a rigid plastic, usable as a glove. Plasticisers are materials which are added to the PVC to make it softer and more flexible. However, they have no protective properties, so chemical gloves with a high proportion of plasticisers perform poorly as chemical barriers.

  • Due to the number of plasticisers in PVC gloves, they perform very well when they are exposed to cold temperatures. The plasticisers allow them to remain flexible down to -20°C and usable down to -40°C. However productivity will begin to suffer as the glove stiffens.
  • Whilst PVC is flame-resistant and will not set alight, applying heat will result in the production of hydrogen chloride gas which is very toxic when inhaled. PVC gloves should not be used with contact heat applications where the temperature is over 100°C.

Natural Rubber Latex Gloves

As the name suggests, natural rubber gloves are made by processing natural rubber harvested from rubber trees. The natural properties of this latex imbue gloves with high elasticity. However, many end users are moving away from using these gloves due to the potential allergic reactions to the natural proteins within the latex.

  • The natural elasticity of NRL helps the glove retain its properties when exposed to cold temperatures. The glove will remain flexible down to -50°C.
  • Given its natural properties NRL does not perform well when it comes to contact with high heat. When accompanied with a suitable liner, NRL has an operating temperature of up to ~120°C whereby passing this temperature the natural rubber will begin to melt.

Neoprene Gloves

Neoprene is a synthetic man-made rubber polymer whereby its production process imbues the polymer with a robust set of properties. However, there are several caveats with using neoprene.

  • Neoprene performs very well in the cold, maintaining its flexibility down to -50°C. When paired with an appropriate supported internal liner, neoprene is a suitable choice for working in cold environments where there is a liquid/chemical risk.
  • When paired with a supported internal liner which will manage the heat transfer, neoprene performs well against contact heat. Within EN 407, sufficiently supported neoprene gloves are able to pass the contact heat level 2 test, 250°C. However even though it can pass the test in laboratory conditions, neoprene may start to show physical changes at temperatures above 180°C.
  • To achieve consistent heat resistance, neoprene often needs to be thick and bulky. This reduces the level of dexterity and tactility that the gloves can offer.

Nitrile Gloves

Nitrile is also a synthetic man-made polymer, however it is very different to neoprene. Nitrile rubber (in the gloves) is a copolymer of acrylonitrile and butadiene. The proportion of components have a drastic impact of the gloves fit, feel and performance.

  • Nitrile is a polymer which does not perform well in the cold. Down to temperatures of around 5°C the glove is usable. However any temperature below this, the gloves physical properties will start to be compromised. Between 0°C and -15°C the gloves will become very stiff and impede dexterity, tactility, and productivity. Below -15°C the gloves will become brittle and become a penetration risk due to the polymer cracking, causing holes.
  • When accompanied by a suitable supported liner, nitrile will comfortably perform in temperatures up to 100°C. As the exposure temperature increases, nitrile will begin to thermoset. This is a process whereby the glove will begin to harden and then not return to its soft state even after the polymer has cooled down. Constant exposure to higher temperatures will begin to degrade the polymer

How is contact heat measured?

EN 407 is the EU standard (adopted by Australia as AS/NZS 2161.4:1999) which covers the performance of materials when exposed to contact heat, amongst others. This contact heat test introduces the sample material to a hot plate at a set temperature and then measures the temperature increase on the inside of the material. It is measured by how long it takes for the inside of the material to increase by 10°C.

If the temperature inside the glove takes longer than 15 seconds to increase by 10°C, then the glove passes the level it was tested against. The levels are 100°C, 250°C, 350°C and 500°C, being labelled levels 1, 2, 3 and 4 respectively.

Another prerequisite to pass the EN 407 contact heat test is to ensure that the glove does not degrade during the test. The samples are visually checked after the test to determine whether the glove melted or developed holes as a result of exposure. If either of these are present, the glove will not pass.

As with all EN tests, the tests are designed to allow for comparisons between materials in a laboratory conditions and do not necessarily relate to real word applications. There are some key considerations to consider when viewing EN 407 contact heat performance scores:

  1. It is a single test against the required test temperature and does not take into account heat buildup over repeated contact with a heat source.
  2. The test only looks for an increase in 10°C between the inside and the outside of the material after 15 seconds. A glove which passes with 16 seconds will still be allowed to show the EN shield - the same as a glove which passes with 40 seconds.

 

How is contact cold protection measured?

Similar to the EN 407 contact heat test, the EN 511 contact cold test is designed about repeatability in a laboratory setting.

In this test, 2 samples from the fingers of the glove are placed between metal plates which are at different temperatures and the temperature drop across the sample is measured to determine its thermal insulative value. Again, there are a number of key points to take into account when reviewing this test and the results it can give.

  1. Environmental temperature – Convective cold can affect the hand temperature even before contact has been made with a surface. 
  2. Wind speed – High winds will increase the effect of convective cold
  3. Time of exposure – Longer exposure and repeated contact can affect the gloves’ thermal insulation
  4. Activity level – The amount of activity the wearer is carrying out will affect the heat they generate and the thermal insulative properties of the glove
  5. Dexterity requirement of the application – Thicker gloves may keep the hands warmer but may impede the wearer from carrying out their application safely
  6. Water – Contact with wet items can affect the gloves thermal properties after contact with the object has finished

There are 4 levels assessed with the contact cold measurements, again being 1, 2, 3, and 4. These determine the thermal insulation/resistance (R) by measuring the energy transfer per degree Celsius, with values 0.025 R < 0.050, 0.050 R < 0.100, 0.100 R < 0.150 and 0.150 R, respectively. Don't worry about what those numbers mean if you don't understand them - just know that a higher level of cold resistance means that it stays warm longer when exposed to very cold things. 

 

It should be noted that these measurements are all designed around contact temperatures. This is not to suggest that you should, for example, freely stick your hand into a 100°C furnace if you have a glove rated to level 1 - that's not a good idea. Rather, it means that, if you are wearing this glove and touch the outside of the 100°C furnace, or something that came out of it, you should not burn yourself on contact, and it should take at least 15 seconds for your hand's temperature to increase by 10°C.

For further information, view the Ansell Safety Briefing here