The Big Bang doesn’t involve explosions or ignitions.
First of all the confusion of when the Big Bang occurred needs to be addressed.
The Big Bang is commonly attributed as the first event in the creation of the Universe occurring at the cosmological time t=0.
The problem with this notion we have absolutely no idea of the state of the Universe when the cosmological time is t < 10⁻⁴³ s when the Universe was in perfect symmetry and all the fundamental forces were unified.
Our current knowledge of physics breaks down below this time scale and it is pointless of referring to a Big Bang at t=0.
There is another Big Bang that cosmologists are interested in which occurred around
t =10⁻³⁰ s.
This is the
Hot Big Bang which can be explained with current physics in the form of Quantum Field theory (QFT).
In QFT there is no such thing as an empty vacuum, rather a true vacuum is a quantum field of the lowest energy level.
The quantum field in a true vacuum have been confirmed in the laboratory via the
Casimir effect.
A false vacuum on the other hand behaves like a true vacuum except it exists at a higher energy level.
The transition of a false vacuum to a true vacuum releases energy while mathematically complicated can be explained by the
Mexican hat potential.
The Hot Big Bang is believed to be the result of the Universe going from a false vacuum to a true vacuum.
In this case the field associated with the vacuum is the
inflaton field Ф which causes an exponentially rapid inflation of the universe for a brief interval.
Like the ball in the Mexican hat potential, the universe can be visualized as a ball (slowly) rolling down the field; when it reaches the bottom into the true vacuum state it oscillates around the minimum and reheats the universe resulting in the Hot Big Bang.