There is a potential problem using Dammaged EH alone, the unit will explode by any cause that caused the damage, not only due bullets hitting the torso.
For example, you put there a car, order your men to get in, and accelerate crashing against a house. If any of your men gets damaged, BOOM. Of course, same happens when you hit with your car any of the other units. May be you can make this work also with HIT EH, as HIT EH returns also the CausedBy object, if it was simply a collision, causedBy will have the damaged unit, if not, it will have the unit that fired against the damaged unit. You may try to activate both EHs, and dammaged wait a quarter of second before checking a global variable where HIT EH put the causedBy.
You may also adapt this script, not only to engineers, but also to terrorists with explosives around their torso too.