Tasmanian Coroner Stephen Carey has handed down his findings into the deaths of 34-year-old Bruce Beamish, of Turners Marsh, and 40-year-old Adrian Chugg, of White Hills, at Veolia Environmental Services' Invermay plant in December, 2005.

The two contractors were welding an oil level sensor to one of the site's 15m-high waste oil tanks, which required a hole to be drilled into the top of the tank.

But the mixture of flammable vapour and the oxygen concentration from the inflow of air through the hole, combined with the use of power tools, caused a massive explosion.

The force of the explosion threw Mr Beamish and Mr Chugg from their position at the top of the tank, killing them instantly.

An inquest into their deaths was held in Launceston in July, during which several key Veolia personnel were called to give evidence.

Their testimonies form the bases of Mr Carey's findings.

``Knowing the circumstances of how the accident happened ... the actions being performed by Mr Chugg and Mr Beamish were clearly very dangerous and it was perhaps inevitable that what happened would happen,'' he found.

``The critical matter, however, is that I do not believe that they -- nor responsible persons at Veolia -- in fact knew these critical circumstances existed at the time.''