Posted By Rod Peel When I was a young engineer working in the gas industry, I was told that aluminium equipment (particularly ladders) should not be used in Hazardous (Zoned) Areas owing to the energetic reaction on impact with rust (Thermite reaction) and a resulting source of ignition. I am trying to find any reference to this which may indicate if particular aluminium alloys are safer than others and therefore to give me some guidelines on specifying insulation cladding for hazardous areas.

Posted By peter gotch Haven't read these reports but suspect they will conclude that it takes some time for the mixture of aluminium and iron/steel to become a problem. Similar considerations apply to mixing aluminium and steel scaffold components with the potential for weakening of structural components. In practice, the norm is to use steel tubes and fittings to tie lightweight aluminium towers and this is not considered an issue for the short duration that such towers are USUALLY erected. Peter

Posted By John Webster The problem is not related to the long term contact between iron (steel) and aluminium and its alloys. Normal electrochemical corrosion processes will be at work. These may present structural challenges - for example in a marine environment the aluminium could exhibit accelerated corrosion, but not an ignition hazard - UNLESS.... and I will come to that below. It is well known that steel tools present a sparking risk when impacting on other steelwork. Hence the use of non-ferrous impact tools in hazardous areas. As Jay points out, this can also happen when aluminium impacts with iron oxide - rust. In practice, aluminium has a passive outer layer of aluminium oxide, and most steelwork is coated in paint, so the chances of the right conditions being present for a reaction are slim. BUT, where there is movement between the aluminium and rusty iron, the surface of the aluminium can be exposed. If this fresh aluminium then grinds or impacts with rust with sufficient energy it could trigger the reaction and produce sparks. Most hazardous areas I have worked in used stainless steel for insulation cladding - but more from environmental/corrosion and durability considerations, and I doubt if the thermite reaction is a serious issue in this context. However, I would speak to one of the specialist insulation companies servicing the oil & gas industry, such as Salamis in Aberdeen. John