a zap from an old car coil is a shocker shure, unpleasant but not fatal to the healthy BUT a lot of coils on modern engines give a real HUGE belt and can be !
The average commodore is one for instance.
BE CAREFUL - Dr Frankenstein !
I hate mats, as they produce to me a uniform flat as a pancake surface. might be good for simulating a tennis court or a bowling green, parhaps a golf hole.
There was a "build it yourself" article in the first issue of I think branchline modeller(or is it Austraklian Railway Journal?). My impression is it is not worth it, the do it yourself article does warn those of delicate hearts that one could get zapped by the makeshift device. Enough said I think !