A council officer gave the order for the fireworks to be let off to prevent crowd unrest, a report found.
But John Satchwell gave the go-ahead at Brunswick Park in Wednesbury amid safety concerns being raised by pyrotechnicians.
The parks and countryside manager even said he would 'take responsibility' if anything went wrong. People were hurt when stray rockets flew into spectators at the display in November 2014, as organisers struggled to contain the huge crowd.
Pyrotechnicians were unhappy that spectators were too close to where the fireworks would be lit, the council report investigating the incident said.
One man was left with a perforated eardrum after being struck by a firework while a 23-year-old man and a seven-year-old girl were also injured. The bonfire and fireworks display was subsequently axed from Brunswick Park.
The report has lifted the lid on discussions that were held between those in charge of the event, including Mr Satchwell, as they began to become concerned about the number entering the park.
Around 12,000 people descended on the park on the night, more than double the amount from the previous year. People were stood in an area close to where the fireworks would be lit where spectators were not supposed to be stood for safety reasons.
The report said attempts were made to clear the area. Wardens were met with abuse when trying to shift people from the area. The crowd was pushed back 'until it was impossible to move them any further due to the density of spectator numbers' before barriers were put up.
The report said: "John Satchwell took the decision to commence the display at 7.50pm and stated that he would take responsibility. The decision was made due to the possibility of further crowd unrest."
Spectators should have been at least 50 metres away from the display. The spectator who suffered a perforated eardrum was 41 metres away.
Councillor Maria Crompton, cabinet member for highways and environment, said: "While extremely regrettable, the incident was the first of its kind at our bonfire events, which we have hosted for 40 years."
"Following the incident, an extensive investigation was carried out. We have since reviewed the suitability of Sandwell's parks for hosting special events."