asbestos, page-21

Just because the contractors are doing the work, does not mean that they are solely liable (and I'm not saying that they are either.)

There is a rather well known case in negligence that has some relevance, Burnie Port Authority v General Jones 1991. General Jones property was stored on site at the Port of Burnie's premises. Burnie hired contractors to do some work, who then proceeded to burn the building down (by accident) when flammable material caught alight from welding sparks. As a result, General Jones' property was destroyed or damaged. In the Supreme Court, Burnie Port Authority was found liable.
(This is a very basic run down, please see below links if you want to get a better idea of how the courts made their decision.)

"Burnie (Port Authority), by allowing its contractor to introduce dangerous substances and activities on site, owed a duty of care to Jones to take reasonable steps to prevent fire, and the breach created liability under the normal rules of negligence..."

Summary of the case:
http://en.wikipedia.org/wiki/Burnie_Port_Authority_v_General_Jones_Pty_Ltd

http://www.austlii.edu.au/au/cases/tas/TASSC/1991/85.html

Further info:
http://revofneg.treasury.gov.au/content/Report2/PDF/NonDelegable.pdf