Why should you never put a knife in a toaster?

The nichrome heating elements are live at mains voltage and are not insulated — the mica sheets they are wound on insulate them from the case, not from you. Touching one with a metal utensil creates a direct path from mains to your hand.

Why it happens

Unlike most appliances, a toaster's heating elements are bare conductors sitting in open air a few centimetres from the slot. The nichrome ribbon is wound on punched mica sheet, which is an excellent high-temperature insulator between the element and the chassis, but there is nothing between the element and the bread.

Switching the toaster off is not sufficient protection. Many toasters switch only one pole, so part of the circuit can remain live relative to earth even when the lever is up and the appliance appears idle.

The same reasoning applies to crumb build-up: accumulated crumbs sit directly against live elements, which is the main fire risk in a toaster and the reason the crumb tray exists.

What to do about it

1. 1Unplug the toaster at the wall before putting anything into the slots — not merely switch it off.
2. 2Use a wooden or plastic implement even when unplugged, and turn the toaster upside down to shake stuck items free first.
3. 3Empty the crumb tray regularly. It is the only maintenance a toaster realistically needs.