Cheers Wilky. I now know where to go for all my lifting certs and questions.
In this case it is not the use of chains per se but chains for this particular task ie making and beaking joints on the drill string. If you haven't seen it it involves throwing a chain at a joint so it wraps around several times so a load can be pulled on it to torque the joint. One end is fixed to the catworks and the other end is loose with just the friction of the wraps to provide the location for the chain. Bloody dangerous!