Posted By Joe
My company use a quantity of galvanized steel ladders, the galvanizing process consists of aluminium and zinc. A question has been asked as to the suitability of the ladders for use in the petrochemical/ oil industry as the aluminium could pose a threat of ignition. Firstly the ladders are not aluminium they are galvanized with aluminium content, secondly I though the risk of ignition from aluminium was dispelled as a myth.

Would appreciate any guidance available on this subject or shared experiences of a similar matter.

Regards
Joe

Posted By Joe
First time for me too, it was the aluminium content that triggered question.
Not being an expert in the galvanization process and the variations in content and percentages it leaves me in the dark as to the correct response.
I understand the percentage is 55% Aluminium/ 44% zinc and the rest ? How much difference this make not sure

Posted By Robert K Lewis
Sorry that should have read that the steel will promote the breakdown of the aluminium present in the coating.

Bob

Posted By ChrisLFAnderson
The purpose of applying aluminium and zinc coatings on steel ladders and steel gratings is that they become galvanic "sacrificial anodes" which waste away in aggressive atmospheres and thus protect the more "noble" cathodic steel structure.
Following extensive testing at the Buxton safety in mines research establishment in the 50s, hydraulic pit props and tirfors made of aluminium were banned from gassy UK coal mines. This ban resulted, for example, in special non-foil wrappings on Kit-Kat biscuits. The justification was that a "smear" of aluminium on top of rusty steel which is then struck by a steel object could cause a chemical Thermite reaction which is able to produce white sparks, hot enough to ignite methane, whereas rusty steel striking rusty steel produces red sparks which do not.

Many Western European countries followed the UK line, while the USA and Eastern European countries did not. Despite this clear difference in the presence or absence of aluminium in coal mines, there appears to be no evidence available that Thermit sparking from the underground use of aluminium equipment has caused methane explosions. Thermit (a mixture of powdered aluminium and iron oxide) is routinely used to produce molten steel to weld railway tracks. In the early 70s the fear of similar problems led to aluminium ladders and scaffolding being banned from UK (and other) offshore installations. More recently, the HSE Offshore Technology Report 2001/017 requires that "aluminium alloy components should not be taken into hazardous areas unless special precautions are taken to ensure safety. It is recommended that equipment containing light alloys (e.g. aluminium ladders) should only be permitted in hazardous areas with the specific authority." Other research suggests that the problem may be more theoretical than real. Some contrasting information, together with a supporting risk assessment can be found at www.afsa.org.za

Kind regards