While this was happening, liquefied petroleum gas was leaking from a tank that was stored with several others in a supply room underneath a part of the grandstands.

[1][2] This was the first performance of the ice show's scheduled eleven-day run in Indianapolis,[3] and the coliseum promoted it as part of its "Shriners Night".

[10][3][4] The initial blast lifted approximately 700 square feet (70 m2) of floor and launched debris and spectators towards the ice rink.

[8] Shortly thereafter, a load-bearing wall underneath the stands gave way and caused an additional cave-in of about 500 square feet (50 m2) of floor.

[10] A few minutes after the initial blast,[note 2] a smaller explosion occurred that produced a fireball that rose 40 feet (10 m) high.

[11][4][2] The location of the explosions had left a crater measuring approximately 50 feet (15 m) across that contained a great deal of rubble and a small fire.

[18] Around this same time, additional crisis organizations in the area, such as The Salvation Army and the American Red Cross,[19] were alerted to the situation and began to mobilize,[12] sending some of their personnel to the coliseum to assist.

[20] The Indianapolis Star would have over 40 employees work to have the story quickly added to the next morning's paper before the press deadline of 1:30 a.m.[21] At 11:23 p.m., a police car at the scene radioed a request for cranes and tow trucks to be sent to the arena.

[16] IFD dispatchers radioed the Indianapolis Fire Chief Arnold W. Phillips[2] and called for an additional engine and rescue squad to go to the coliseum.

[25] The fire chief ordered that heavy equipment be brought in to help free some of the injured spectators from the rubble, as the firefighters' electric hacksaws had proved ineffective.

[18] Meanwhile, Civil Defense officials began sending their own emergency equipment, primarily focusing on tools that could remove the debris.

[23] Around 11:35 p.m., they contacted the police department of nearby Speedway, Indiana, and requested that they borrow a mobile crane from a local heavy equipment company.

[23] As a result, Civil Defense officials began directing ambulances to enter the fairgrounds on the north side and exit to the west.

[28] Civil Defense officials began directing some ambulances to take their injured to a nearby military base to avoid possibly overcrowding local hospitals.

[24] Shortly after midnight, the superintendent of the Indiana State Police,[24] as well as the Salvation Army's canteen truck and nurses from the American Red Cross Motor Corps, arrived at the fairgrounds.

[31] At 1:47 a.m., the police chief, attempting to reduce traffic congestion around the arena, barred any additional vehicles from entering the fairgrounds.

[38] At about 3:00 a.m., some relatives of those thought to be dead from the explosion began to arrive to identify their bodies,[39] and half an hour later, a press conference was held wherein the command post gave updates about the state of the response and answered some questions regarding the cause of the incident.

[57] The cause of the explosion was identified as the five LP gas tanks, each with a capacity of 100 pounds (45 kg) of propane,[20] that had been recovered and moved to the Fire Headquarters.

[58] This was confirmed in a technical report issued by engineers from Purdue University on December 4, 1963, that said that LP gas that had leaked from the tanks was the most probable cause of the explosion.

[59] These tanks had been stored in an unventilated[3] concessions area storeroom,[36] which was located directly beneath the southeastern section of bleachers.

[2] Ultimately, this gas came into contact with a heating element on an electric popcorn warming machine and ignited, causing the initial blast.

[4] Following the explosion, a grand jury was convened by Marion County Prosecutor Noble R. Pearcy, and they took five[note 6] weeks to announce their findings.

[68][47] Involuntary manslaughter charges were pressed against three individuals from the company that had supplied the LP gas tanks, the Discount Gas Corporation, and two employees of the arena's operators, the Indiana Coliseum Corporation (the general manager and the concessions manager),[60] while misdemeanor charges were pressed against Fire Marshal Anderson and Fire Chief Phillips,[2] the latter of whom was indicted for failure to inspect the coliseum.

[59] The grand jury also criticized the Indiana Coliseum Corporation for its "steady build-up of indifference and carelessness in the unlawful handling and use" of the gas.

[63] Additionally, despite evidence that showed that the coliseum operators had been warned about gas problems in the past, the others that had been indicted had their charges dropped because they were found not to have had a direct role in the explosion.

[63] In the end, only one person, Discount Gas Corporation's President Edward J. Franger,[63] was found guilty by a jury, in this case of the lesser charge of assault and battery.

[75] On December 12, about six weeks after the accident, the coliseum hosted its first post-accident event, a two-day Polled Hereford cattle show.