Applications involving high levels of radiant heat may require specialized garments with aluminized fabrics to reflect heat energy. Selection can be made according to the needs of the application, such as the level of heat energy, the duration of exposure, the need for a moisture barrier and so on. However, there are several key considerations to keep in mind:
There are individual tests for convective, radiant and contact heat, and two further tests for molten metal splash (iron and aluminum).
Each of the three heat resistance tests places fabric between a heat source and a calorimeter, recording the time until a specific rise in temperature is achieved. The longer it takes to record the rise in temperature, the better the fabric is at resisting energy transfer, offering a higher the level of protection. Results are classified as Class 1, 2 or 3 (3 the highest) according to times indicated in the standard. However, the radiant heat test (ISO 6942 Method B) features the four classifications described below.
The introduction to the standard explains that Classes 1, 2, and 3 can be generally referenced as levels of protection for low, medium, and high-risk applications, but the fourth performance level is used for radiant heat. Class 4, recording a time of over 95 seconds, is specifically designed for high radiant heat applications and testing of aluminized garments. Aluminized PPE should achieve Class 4 (a result over 95 seconds).
Clothing to protect against high levels of radiant heat relies on the fact that it can be reflected by a shiny surface, meaning that high heat PPE is commonly constructed with reflective materials. Gold, having a very high reflectivity, would be an ideal choice and a thin layer is often used on visors. However, gold is too heavy, and too expensive. Aluminum is light, flexible, and relatively inexpensive, making it a reliable and cost-effective choice.
Aluminized garments can provide sufficient reflection of heat energy to protect workers from high heat hazards. Depending on the intended application, aluminized fabric may feature one or more layers.
Not all aluminized garments feature 100% aluminum surface. In some cases, to reduce cost, manufacturers use a fabric that is a mix of aluminum with a polymer. This does reduce the price, but it also reduces the reflectivity and can result in lower performance. For this reason, especially with cheaper high heat protective clothing, it is important to ask if the surface is 100% aluminum. You should also ask how the fabric performs in a Radiant Heat Resistance Test.
Aluminized clothing often comes in a coat and pants configuration, with separate boots, gloves, and a hood with visor. However, there are important considerations for users:
Thus, selection and use of garments should only be undertaken following a risk assessment, considering all relevant factors, by qualified safety personnel.