There is an extremely good thread in the tree care forum on sounding.
It is very well presented and a huge amount of good information.
i posted this thread purely to draw attention to something I feel is very important and that, I know experienced fallers/cutters/arb guys do it as part of their procedure and it will be taught it the courses provided to folks coming into the industry, however I feel it should be drawn to the attention of less experienced and guys starting out in the industry as well as any home owners contemplating falling/cutting a tree.
It is extremely important that a tree is checked for soundness as well as any visible defects or/and hazards BEFORE any cuts are made as a tree may look healthy etc but for example it might be hollow or partially so or have a rotten or partially rotten heart which might not be readily visible. Thereby the approach will be different.
A real life incident (just to possibly illustrate to who this is aimed at)
I falled a small birch last year when I was over here on business ( bout 24-26" on the butt by round 36' plus twigs, so not big or high) it looked at first glance that there was nothing amiss it had full leaf and had stood up thru the storms over here. It was on a fence line and leaning slightly nothing major and looked like it could be falled like any back leaner in such a position. However when the home owner checked it - he cuts and does his own firewood and is able to cope with things, he has spent time with me and experienced me banging on endlessly bout safety and falling procedures - he heard a hollow sound when he tapped it so he asked me to have a look and yep it was hollow and it would never go the way he had intended as the face would have been sound if cut normally but the holding wood would not have existed nor much backwood so if he'd bashed on a fence would have been damaged and a red face would have resulted at best at worst a trip to the hospital or morgue at worst.
I falled it (it doesn't matter what cuts etc I used that is not important)
The moral here is read the thread on sounding trees (I know it detailed but knowledge saves folks being hurt) and please less experienced guys practice this it will at some point save ya from insurance claims and being hurt or someone else being hurt) and home owners don't bash on please get some one who can cope with these circumstances as better a paying a pro than paying for a damage or a life in pain.
If this offends then I make no apologies as good practice no matter where in the world saves injury,damage and lives.