To be fair Water System, Imran posed a question, and you have evaded it.
Chris also posted factual evidence of a header tank distorting and spilling its contents over a child that slept below.
Please correct me if I am incorrect, But the laws in this country, regarding unvented cylinders are somewhat more fail safe than in other countries.
I base this fact on unvented cylinders failing in other countries, but not here in this country where the unvented cylinder was created.
With all due respect Water Systems, lets deal with malfunctions of cylinders and systems as they occur in this country first, prior to second guessing systems that have yet to fail.
The fact that unvented cylinders could possibly explode in this country is feasable, but has not happened.
The fact that vented systems has claimed lives is true and evident. Would it not be sensible to address these issues first.