A common 1/4 stick fire cracker as the detonator and model rocket engine
nichrome wire igniters wired to energize from a safe distance away. You
have to pack the mixture pretty tight with the fire cracker in the
middle. Wrap the nichrome igniter wire around the firecracker's fuse,
run your wire out a safe distance, connect wires to battery terminal and
key operated switch / covered push button combination, make the needed
safety announcement, when all check points report all clear insert and
operate the keyed switch, begin countdown, press button.

Firecrackers are not readily available here but I will give it some
thought. Knee replacement is on the schedule for next week so the lab
work will have to wait...

John Ferrell W8CCW
"Life is easier if you learn to
plow around the stumps"