Hydrogen Gas

The way you put it should make any less than full container with diluted H2SO4 impossible. In other words, battery acid would not be available in say 20 or 50 gallon containers? Well you can buy and store this. You'll need to be more careful to not spill the liquid, rather than what your explosiveness theory concerns. This battery acid comes in plastic drums that resist the acid.

The H2 is not a specific problem and comes free in the battery when changing the state of charge. SOG. and escapes to the air with open battery configuration.

It would be simpler to open the vent on the stack. Hydrogen is a light molecule. Its molecular velocity at ambient temperatures exceeds the escape velocity of this planet, which is the reason why there is very little molecular hydrogen in the atmosphere during this epoch.

So forget the fan. Just ventilate the tank to atmosphere outside the building.

If this cannot be done for some unknown reason, while ventilation with air will tend to reduce the hydrogen concentration and hence the explosiveness, it would be better to ventilate with something inert, like nitrogen, thereby removing one of the three items in the Fire Triangle - the oxygen in the air. Be careful where any vents go from nitrogen-blanketed vessels as nitrogen itself is an asphyxiant. The issue of pressure control is important, as the tank lid is likely to be of size and one doesn't want "flying saucers" in the plant.

What is curious is why these issues didn't appear during the original Process Design, particularly the HazOp Study.

If the hydrogen is not being produced by the intended process, then it is the product of corrosion of the plant with acid. If this is so, then there is a serious materials compatibility issue that requires immediate resolution.

Keeping the tank filled is not an option, as the whole purpose of a tank is to allow level to go up and down.

Why can't the process be reconfigured such that the tank is unneccessary, on the basis of "what you don't have, can't leak"?

If in doubt, consult a qualified Chemical Engineer locally.

Just light a match.

And catch the next train out of town.

I would agree with others the presence of hydrogen occurs due to deterioration of carbon steel, but if the tank is properly designed for it's purpose, corrosion allowance for design life has been made....The venting should be at the highest point of the tank, should be at least 6" in diameter, be goosed to prevent water ingress via precipitation, have a screen insert to prevent birds (etc) from entering, and exhaust in an area that is not near personnel.....

http://www.sulphuric-acid.com/techmanual/Storage/venting.htm

http://www.sulphuric-acid.com/techmanual/Storage/storagetanks.htm

You don't state the headspace pressure, which is quite important. You also don't state the temperature which is also important.

If this is a condition at the end of a batch reaction, there are a number of ways that you could proceed. However, it depends on the tank pressure and temperature AND a more precise concentration of the H₂SO₄ in the liquid phase (a range here would be acceptable), and concentration of H₂ in the headspace.

The thermodynamics of the system must be considered before a determination of depressurization/venting/purging procedures may be advised.

In short, NEED MORE SPECIFIC INFO!

HINT: You can never have too much information; er, well non-personal anyway!