The display injured some in the 50,000-strong crowd as they gathered for the Bledisloe Cup test at Eden Park in August last year.

A fireworks stunt that went "catastrophically" wrong at an All Blacks game has cost a pyrotechnics company $100,000.

The display shot shrapnel at the 50,000-strong crowd as they gathered for the Bledisloe Cup test at Eden Park in August last year, injuring three spectators who suffered permanent scars.

It was "clearly good luck" that more people weren't injured, or even killed, Judge Grant Fraser told the Auckland District Court on Thursday morning as the responsible company, Waikato-based business Van Tiel Pyrotechnics, appeared for sentencing.

BEVAN READ/FAIRFAX NZ Van Tiel Pyrotechnics appeared for sentence at the Auckland District Court, pictured, on Thursday.

The business earlier pleaded guilty to seven charges laid by WorkSafe, a lead charge under the Health and Safety Act of failing to take all practicable steps to ensure no action or inaction of any employee harmed any person, and six under the Hazardous Substances and New Organisms Act, including failing to ensure hazardous substances were correctly identified.

The court heard the company, headed by director Martin Van Tiel, was contracted by the New Zealand Rugby Union (NZRU) to create 12 fireballs around the field, with one directly behind the All Blacks due to light up as the team finished the haka.

The fireballs were created from a device that charged fuel in plastic mortars, igniting the firework upwards, Worksafe counsel Ian Brookie said.

On the day in question, the fuel the company usually used had run out and "significantly" another pyrotechnic fuel called 'the red star' was used, grabbed from a bucket with a handwritten label, he said.

The red star had a higher explosive classification but wasn't properly identified on the label.

Once compressed into the mortar, the mix became contaminated and instead of shooting upwards, it exploded inside the mortar, sending metal pieces, including a 30cm spike, flying into the crowd, according to the summary of facts.

"The stakes were high for the work the defendant was doing, a mistake by way of contamination could well, and did in this case, create a substance with a mass explosion hazard," Brookie said.

Three spectators were hit in the face, including rugby fan Cecilia Wang who required stitches to a 9cm gash on her forehead. Another passed out after being struck.

One of the victims had flown from Sydney specifically to see the game and said he was "shocked" with the consequences.

All three victims had permanent scars and suffered ongoing emotional harm from what they described in victim impact statements as a "nightmare".

Brookie said Van Tiel fell "well short of the mark" when it came to fundamental tracking, identification and labelling procedures around explosives, but Van Tiel's lawyer, Neil Beadle, said in his client's 20 years of pyrotechnics business, the incident was a solitary and "unfortunate" one.

The company had been putting on fireworks for the NZRU for a decade, the fireworks substances were all stored correctly at their location and staff were trained to be skilled in their handling and identification, Beadle said.

Van Tiel had been a "responsible" defendant who had apologised personally to each of the victims. One had been given an undisclosed reparation package, and another was flown to Wellington to watch another match, Beadle said.

Considering the total fine and reparation the company should pay, Judge Fraser said, "Let's cut to the chase. This is a classic case of human error.

"A human put the wrong mix into the mortar which resulted in catastrophic consequences and I agree it could have been significantly worse, and even fatal," Judge Fraser said.

He acknowledged the company had since implemented further steps to ensure an incident of its kind wouldn't happen again.

For the health and safety offence he ordered a fine of $52,500 be paid, and for the hazardous substance act charges, a fine of $31,500.

Reparations of $3000 each were to be paid to two of the victims, along with additional costs of $2282, said to cover the financial loss the victims had suffered.

Combined with a reparation already made to a third victim, the amount of which wasn't disclosed in court, Judge Fraser said the total to be paid was "in excess of $100,000".

"The court acknowledges the steps now taken by Van Tiel to prevent anything like this happening again," he said.

Speaking after the court appearance, WorkSafe chief inspector Keith Stewart said investigations revealed systemic failings in the company's standard operating and quality control procedures.

"The fireball devices that failed were manufactured by the company using the incorrect mix of substances. This produced contaminated fireball devices that were highly explosive and dangerous.

"The company had also failed to properly label explosive substances and had inadequate tracking systems for its hazardous substances and pyrotechnic compositions."

Stewart said the devices were dangerous and it was fortunate that the injuries weren't life threatening.

Van Tiel was present in court but declined to comment.