Eric - the NCB did accept responsibility. I was employed (with others) as a scientist after the disaster to work on projects leading to increased tip safety. Many new rules were created for the safe construction of tips, the tips then in existence were all surveyed and assessed and and the dodgy ones were all regraded and rendered safe. It's just a pity the NCB didn't do it in 1947 at nationalization - but some of the tips had been there for a century or so, and no one thought anything about it. I believe the tip that collapsed had been there since well before the existence of the NCB.
I've signed the petition.
Ray