Depends on what your pickling…
Metals in acids react to give off hydrogen
Carbonates.. ( some fluxes) give off carbon dioxide…..
A part from water vapour
and a little mist of acid ,..thats about it

Hi Jason,

Metallic copper will not react with acids to produce hydrogen. Acids will dissolve copper oxide, without producing hydrogen and they will react iron ,steel, zinc and aluminium to produce hydrogen. Only oxidising acids such as nitric acid will react with copper but they do not then give off hydrogen but some reduction product like nitric oxide.

If you are pickling with citric acid normal sized ME objects, ie less than circa 0.5 square metre surface area it is unlikely that hydrogen build up would be a problem. Because hydrogen is so light it disperses very rapidly. However, it is prudent to take sensible precautions to avoid build up in confined spaces ie do not cover containers, ensure good ventilation etc. and avoid naked flames and sparks.

Mike

Adrian,

Appreciate we are probably only talking about small amounts of gas here , and the risk of an untold occurance is therefore low , but would still like to supplement the excellent information and guidance already offered. Think your decision to work with an open door is a most prudent one . Regarding the hydrogen , please note that IT burns with an invisible flame , which is why we were instructed to approach a suspected hydrogen fire with an outstreched roll of paper so that it would act as an indicator. With respect to the nitric oxide ( nitogen monoxide ) , please note this really can be rather naughty. It is an oxidiser , corrosive to the respiratory duct , and can also cause severe skin burns as well as eye damage . And then , just by way of a bonus, it can cause / intensify a fire. Given all these issues , I believe good and consistant ventilation to be an essential requirement. Just by way of a small additional piece of information , at work we were unusual in that we had a fully piped nitric oxide system ( arranged in 2 x 4 banks of equivalent J size cylinders) feeding into the neonatal critical care unit . For a number of reasons its use was discontinued and we reverted back to the original very small cylinders.

Trevor.

Edited By Trevor Drabble on 19/02/2014 00:47:43

Not only is Hydrogen very light compared with the atmospheric gases but its molecule is very small. That means a Hydrogen molecule will travel a long way before hitting an Oxygen or Nitrogen molecule. Therefore any Hydrogen will disperse widely and quickly into the atmosphere and disappear.

Keep the door open anyway.

JA

Some ballpark numbers – citric acid is trihydric with a molecular weight of around 200. So 200 grams of acid could potentially yield about 1.5 mols of H2, or around 30 litres (0.03 cubic metres) at STP. That would be 3% by vol in a 1 cubic metre space, just below the lower threshold for a flammable mixture given by Nicholas above. Say a double garage has a volume of 30 cubic metres. It would need 30*0.2 = 6kg of citric acid to be consumed to get to the 3% level – assuming the garage is hermetically sealed! So I doubt there is a problem.

Regards, Bob