DAVID Copperfield has been forced to reveal more of his magic secrets as he testified in a lawsuit brought by a British man who was injured at one of his shows.

Taking the stand in a Las Vegas court, the magician said that he believed no one had been injured in 20-years of his signature vanishing act. He also was forced to tell the court how audience members were picked for the illusion, which is known as “Lucky#13”.

Copperfield said he and stagehands assessed the capabilities of audience volunteers as they approached the stage, climbed stairs and seated themselves in a boxy 13-seat apparatus for the illusion.

“Seven times, we make an assessment. Visually watching them interact with their footwear. It’s like seven different screening moments,” Copperfield said.

“If those shoes created a challenge, I would look carefully and see how they rock those shoes and I would know whether or not they would be able to do the piece.”

The jury was told that some volunteers were turned away.

Over the objections of Copperfield lawyer Elaine Fresch, Morelli asked Copperfield if he thought the number of people not injured by the illusion over the years suggested it was safe.

“I’m not in the business of hurting people,” Copperfield said.

“The illusion must be safe because of how many people have done it without getting injured?” Morelli asked.

It comes as lawyers for the British tourist who says he was badly hurt taking part in an illusion by Copperfield in 2013 say they’ve found three other people who were injured in shows over the years.

Lawyer Adam Deutsch told a judge overnight that each is willing to testify before a jury that has heard Copperfield and the show’s executive producer deny knowing of anyone being injured during more than 15 years performing the trick.

Mr Deutsch says the three, all women, came forward after hearing about Copperfield’s testimony in the ongoing negligence trial.

Judge Mark Denton ruled that before they testify, the women should be questioned under oath by defence lawyers for Copperfield, the MGM Grand resort and several corporate entities facing civil damages claims.

On Tuesday, the magician insisted he knew of no one being injured during more than 15 years of performing a signature vanishing act at the centre of a lawsuit by a British tourist who claims he was seriously hurt in a fall during a Las Vegas performance.

Amid complaints from his lawyers about widespread media coverage, the world-famous illusionist returned to the witness stand, telling a Nevada jury about the trick that makes people seems to disappear on stage and reappear in the back of the theatre.

At least 55,000 audience volunteers have taken part in the illusion over 17 years, according to Copperfield and show executive producer Chris Kenner, who testified last week.

In 60 to 90 seconds, stagehands with flashlights ushered randomly chosen participants past dark curtains, down passageways, around corners, outdoors, indoors and through an MGM Grand resort kitchen to re-enter the theatre and “reappear” for the show finale, according to testimony.

Copperfield remains on stage the entire time.

Benedict Morelli, lawyer for plaintiff Gavin Cox, has characterised the route as an obstacle course and the pace as dangerously fast for people who might not have appropriate footwear and are not told in advance what they will encounter. Copperfield said he and stagehands assessed the capabilities of audience volunteers as they approached the stage, climbed stairs and seated themselves in a boxy 13-seat apparatus for the illusion. The trick is dubbed “The Thirteen,” for the number of seats.

The jury has been told that some volunteers were turned away. Over the objections of Copperfield lawyer Elaine Fresch, Morelli asked Copperfield if he thought the number of people not injured by the illusion over the years suggested it was safe.

“I’m not in the business of hurting people,” Copperfield said. “The illusion must be safe because of how many people have done it without getting injured?” Morelli asked.

“Numbers are not a defence,” Copperfield said.

Copperfield said he didn’t know Cox claimed to have been injured in November 2013 until he was sued the following year. He said he stopped performing the illusion a year later.

Cox alleges he fell after being hurried by stagehands through an alleyway coated with a powdery residue near a trailer-sized trash bin. The resident of Kent, England, claims lasting brain and bodily injuries from his fall have cost him more than $US400,000 ($525,000) in medical care.

Fresch lost a bid on Tuesday for a mistrial based on the amount of media coverage about the case, including interviews involving Morelli.

Clark County District Court Judge Mark Denton allowed testimony to resume after asking jurors if they saw news items about the case during a five-day break in the civil trial. Three said they turned off broadcasts when they encountered them.

Copperfield’s lawyers lost pre-trial motions to close proceedings to the public to avoid giving away performance secrets.

A state appeals court ruled on Friday that Denton can close the courtroom to the public for some testimony to protect tradecraft.