Well, let me first start by saying, any & all snakes pose some sort of risk (even if small, at least that's my mindset).
Now I've had the unfortunate experience of being bit by 2 different burms, one 7ft the other 9ft. Both were rescues, the smaller bit me on the day it was to be fed, and was definately my fault (although my stupid girlfriend at the time didn't help things!). She was all excited to feed him, but I didn't have the forceps nearby, but she really wanted to feed him so I went ahead and did it... yep, instead of nailing the rat he nailed my hand!!! He wouldn't let go, wrapped his entire body around my arm, hurt like HELL!!! Eventually got him off by running water in the bathtub and submerging his head underwater, proabably was on there a good 5 minutes. (My girlfriend actually said, 'what do you want me to do, cut his head off?!?!' yeah honey, like you could do that!). Once let go he slitered back into his cage, where the rat was now laying, and ate it!
The second experience was much scarier. I rescued a 9ft albino burm that was near death, had mouth rot, mites, severely emaciated (it was 9ft and barely 25lbs, very sickly looking), the people I picked it up from said it was mean, but it was nearly dead when I got it (free roaming a basement with no heat). Took it to the vet, got it subcutaneous fluid injections, a topical cream/anti-biotic for it's mouth, and gave it shots every 3 days and it looked tons better from the get go, but refused to eat for 2 months. Then my roommates and I realized it would follow us as we walked by, then it began striking at the cage as we passed by (needless to say it was now eating... very healthly I might add). Since it was healthy, it was time to place it in a good home, found an experienced reptile facility back east and was to send it to them. The day before I was making sure the box I had was the right size, opened the cage, then positioned the box then... WHAM!!!! I saw a 9ft streak of yellow screaming towards my face, lower jaw landed just above my right eye, top jaw about half way up my head, I threw my hands up and the rest of his body wrapped my right arm. I screamed, blood everywhere, went into the bathroom, my roommate ran the hot water, wrapped my other hand in a towel and soaked it, then stuck it in the snakes mouth and pulled it off my head (I could feel the teeth pop out one at a time... pop... pop... pop!). He slithered back thru the blood (must've looked like a crime scene) straight back into his cage. Had a pretty nasty mark for 2 weeks, but no scar... I got lucky!!!
Ryan