Did something similar in 82, as an apprentice in a drawing office of a HV switchgear company, I was using a retractable stanley knife to cut electrical tape and that film that is used to create copies of the original, and you scratch the parts out that are being changed and replace on the other side the other version in ink or plastic pencil, anyway it was on the desk with the blade out obviously, my elbow caught it and it slid of the desk and landed in my right leg, bouncing out and falling on the floor, after looking down I noticed the cut in my jeans and calmly collected some electrical tape and headed off to the toilets, whereupon I quickly bandaged the cut up with toilet tissue and the tape and then headed off to the on site medical centre.
A couple of days later whilst visiting the centre again I said - it's feeling lumpy, as I squose the area, a jet of plasma shot out and just missed the nurse who was just about to bend over to look at the wound, luckily the wound only went as deep as the dermas so no blood, i too still have the scar.