the igniter is made of a wire with paper tape holding it$.$ In the head of the igniter is a very thin wire surrounded by pyrotechnic material. Pressing the second switch allows more current to flow through the igniter. Why does it        burst into flame when the both switohes are pressed but not when only switch pne is pressed?

What will happen if the first stch$,$ which is the key, is removed? What will happen if the first switch, which is the first button you press, is not pressed?