Hea about this on the hetas course. I got the impression it had something to do with damp pellet store and decomposition of the pellets, what's your take on it peteheat?
All I can confirm re the Irish case is the pellets were as dry as the sands of the Sahara desert.
I know there can be problems with shipping and storing large quantities of wood pellet, re; the shipping transporting any wood in the hold has been a known problem for years it goes back to shipping large amounts of timber like teak etc which could be in a sealed hold for months.
It appears some people forgot that they were transporting a product that once was live and part of the early decay process is it gives off various gasses one of which appears to be C0, another theory I read was the heat that built up in the hold was a cause, I think it is policy in the shipping industry to ensure the hold is vented for a while to allow air circulate before off loading.
Wood pellet is different because we have all of the above and the heat generated during processing if the fuel is loaded when warm, there have been cases in pellet factories where the large silos for storing the pellets have gone on fire, the explanations I read blamed the operators for not allowing the pellet to cool before loading it into the silos.
For home owners and commercial users the above should never be a problem because the pellet will have had plenty of time to cool as it is very unusual to manufacture and deliver the same day, in fact I have been in very large sheds where the summer production of the wood pellet fuel is stored for delivery in winter.
Having witnessed what I did I would never advise anyone to enter a pellet store connected to a working boiler even if it has broke down before ensuring the tank has been vented and a second person is present, of course that should apply to anyone entering any store that has a limited entry and egress point regardless of the contents.
I'm sure HSE has very detailed documents about the safety precautions we all need to take in such situations.