This article has to do specifically with high heat resistant clothing for foundries and other environments where people work with molten metals or in proximity with industrial ovens or other very hot objects, such as aluminized clothing, or other high-heat insulating clothes/suits. The aim is to provide basic information to help better understand how “heat” works and how to protect from it.
Firstly, you need to break up the heat hazards:
Ambient heat is, basically, the temperature of air in the environment where one must work. This is specifically the temperature of the air (or other gas). Once ambient heat gets to a certain level, it becomes hard or impossible to protect a person without very specialized suits and a system to provide breathable air. If the air is over 200 degrees F, then, even if you can insulate your body from it for a reasonable time, you would also need to breath, and cool-enough air would end soon.
Conductive heat – this has to do with hot an object can be that you can touch with your protective gear without causing the protective gear to quickly deteriorate. In addition to charring, stiffening, or otherwise deteriorating, materials can auto-ignite when they reach a certain temperature (for example, cotton auto-ignites at around 700-800 degrees F). In a way, the ambient heat (hot air) acts on you the same way as conductive heat, it is just that normally the coefficient of heat exchange and heat storage capacity of air is much lower than that of solid objects like metal or stone. Having two solid objects physically touch is normally the fastest way to conduct heat.
Radiant heat can be simplified as energy emitted by a heated object via waves. This is how the sun warms our Earth, or the heat you feel when you are next to a fire or oven. This heat behaves in ways similar to light, meaning that it’s rays can be reflected or absorbed.
Compare to a thermos
To easily understand the different types of protection from heat, let’s consider a thermos with a vacuum layer (you can probably purchase one in a store for your hot coffee). A thermos has an outer solid layer, and an inner solid layer, between them it is ideal to have a vacuum. By having a vacuum, a thermos eliminates any conductive heat transfer from the hot liquid to the outer layer that a person holds in their hand. It means that there is literally nothing between these two layers, so nothing can conduct heat. This leaves only radiant heat. Thus, the hot coffee quickly heats up the inside layer of the thermos, and that layer starts to emit radiant energy, which goes towards the inside of the outer layer. For this purpose, the inner side of the outer layer of your thermos is made very reflective, with a mirrored surface – this makes the radiant energy to mostly reflect from that surface and go right back. All together, this means that the heat cannot easily escape from the hot coffee and does not get transferred to the surface that you hold with your hands.
Same features as thermos in high heat clothing
However, in clothing it is not practical to include a vacuum layer. Thus, the goal is to aim for the next suitable thing – trying to trap as much air as possible. Air is a relatively good insulator, in fact, one of the best insulators that we have. This means that layered clothing or something with a spongy structure performs rather well.
Additionally, in industrial applications, the levels of temperature that can be present get rather extreme. So you need to make sure that your heat resistant clothing will not start to burn, melt, or fall apart when subjected to whatever the temperature you may have in your work environment. You need specialized fabrics that are stable at high temperatures – normally it would be man-made fibers such as Kevlar or other high-tech materials. You need to reasonably judge the temperatures of the hottest objects that a person can purposefully or accidently touch and make sure that the materials that will cover that part of body will be able to withstand that temperature.
Finally, as the heat source is external, you’d need to also protect from radiant heat. For that, you can use aluminized clothing, which has a laminated film of reflective aluminum on the outer layer. The aluminum layer would not be as effective as a mirror, but it is effective in reflecting, normally, over 90% of radiant energy. You just have to make sure to keep it clean and shiny to maintain its radiant heat protection properties.
For radiant heat, you just have to have aluminized outer layer on your clothing, and that layer has to be in good shape to be reflective.
If you have significant risk of touching very hot objects, you need to look at the maximum contact temperatures that the materials can be exposed to. But keep in mind that if a material can touch an extremely without being damaged, it does not mean that it can protect you from that temperature – some thin materials are able to withstand very high temperatures, but they may not offer good insulation/protection from conductive heat, meaning that they heat up fast and the heat get transferred to whatever is under that material layer.
If you need to touch or hold something hot or be in a hot environment for a more extended period of time, you need to look at insulation. For insulation, nowadays, look at very high-tech materials specifically made for insulation (like CarbonX) or look at layering. Aim to layer to trap air, so don’t make things fit tightly. Figure that the outer layer is most exposed to abrasion, so it is good to be able to replace it as efficiently as possible.
Because temperatures get very high in industrial settings, you need to watch out for your own safety even if you wear really high end aluminized clothes or gloves or other high heat resistant garments.
The simplest advice is to avoid contacting hot objects or limiting time of contact/exposure, though, of course it doesn’t always work out.
The second simple advice is to try to wear things you can quickly take off. Heat does travel through any clothing or gloves. You need to make sure that you can easily remove a garment if you start to feel that the inside of it is starting to become dangerously hot. You also need to check whether you can remove the garment without touching the extremely hot outside parts of it with bare hands. A good example of that is loose gloves vs tight fitting gloves – if you have oversize, loose gloves, you can simply shake them off; if your gloves are a tight fit, you can remove the left using your right, but then you may need to pull of the right one using your bare left hand – it may not work so well.
Finally, if you deal with molten metals and have a risk that a molten metal may splash on the person, then look for clothing that is effective in shedding this particular metal from its surface. The goal here is to make sure that the molten metal rolls off from your clothes as quickly as possible and does not get stuck/caught anywhere. If it gets caught, it will mean that it will start to act on a small space, quickly conducting its heat to the inside of the garment in a particular location, and likely burning a hole it it. There are materials that are specifically tested and rated for abilities to shed molten aluminum, iron, and other metals.
You can see Legion Safety‘s products for environments with extreme heat here:
We hope that this has been helpful and will help to keep you safer at your work!
If you have additional comments or advice for people working with extreme heat, please write us an email or leave a comment below so others can see it. We will do our best to investigate and add your insights here!