My advice, tone it down, pieces no more than 10% of blocks SWL or WLL.
Just for clarity and to re-affirm what Treeco wrote.
The SWL or WLL of the block has already been adjusted in.
But where there is no mention or stamping be careful.... like ropes are usually rated breaking strength.
So a 2t block can take 2 ton, no worries, and yes that's only 1 ton a side... however, if the piece you cut is going to dynamic load the block that's where things go way off the scale.
In a vid I'm about to put up you'll see the the block is well below the head I cut out, the forces on the block in that video would have easily gone 7X the weight of the piece, maybe even 10x.
I estimated the piece at being 100kg, a 4' fall to the block, 4' past the block, then braking, I reckon if you dyno'd that load at the block it would have peaked around 1000kg.
But hey, the rope is only experiencing about 1/2 of that, so 500kg on the rope which is rated 6000kg breaking so I'm OK there. The block can take 2000kg all day every day as that's its SWL so 1000kg is OK there also.
But what this all means is KNOW YOUR ****, know your drops, calculate your margins, and
dont have idiots on lowering ropes being BANK ROBBERS!
And you being a deputy sherrif know that
BANK ROBBERS hold everything up!
I have seen 50kn steel biners straightened out, blocks go flying out of trees, lowering devices race up trees and lowering ropes breaking ... all due to overloading. Mind you, not on my jobs.
You need to match your gear, if the block is 2ton then match it with slings and rope accordingly.
Unlike USA we use a 1/6 SWL for ropes. My lowering rope is 6000kg breaking so 1000kg SWL. The rope's SWL should be around half the blocks SWL. (remember the block experiences twice the load of the rope). What attaches the block to the tree has to be equal to the block in SWL. I attach mine with doubled lowering roped so it's pretty close unless you want to argue about loss of strength due to a cow hitch.
Cheers.
Link to video
http://www.arboristsite.com/showthread.php?t=47587