What is a prop gun and how can it kill someone? How the Alec Baldwin tragedy was possible

Alec Baldwin discharged a prop firearm on the set of the upcoming film "Rust" on Thursday, killing cinematographer Halyna Hutchins and injuring the film's director, Joel Souza.

The incident is not the first such tragedy involving a prop gun. Brandon Lee, Bruce Lee's son, died at age 28 in March 1993 after a shooting involving a prop gun. In 1984, actor Jon-Erik Hexum died from a self-inflicted gunshot involving a firearm with blanks.

Many of the details of what happened on the set of "Rust" have yet to come to light. The accident is under investigation, according to the Santa Fe County Sheriff’s Office, and no charges have been filed.

Baldwin was handed a loaded weapon by an assistant director who indicated it was safe to use in the moments before the shooting, according to court records released and obtained Friday by The Associated Press. The assistant director did not know the prop gun was loaded with live rounds, according to a search warrant filed in a Santa Fe court.

"Detectives are investigating how and what type of projectile was discharged," a release from the sheriff's office said.

USA TODAY obtained an email sent to members of IATSE Local 44, a union of propmakers and other craftspeople who work within the entertainment industry, about the incident. The message said that the prop gun from the "Rust" set was loaded with "a live single round" and that no Local 44 members were on set.

Crew members reportedly walked off the set of "Rust" to protest working conditions hours before Hutchins was killed.

According to the Los Angeles Times and Deadline, crew members working on the Western raised concerns about several problems, including safety, before Thursday's accident.

A spokesperson for Baldwin told The Associated Press there was an accident on the set involving the misfire of a prop gun with blanks.

What is a prop gun?

Those less familiar with the lingo used in Hollywood may not have heard of prop guns. A prop gun or prop firearm can mean several different things. The term can refer to fake guns but also real weapons that are being used as props.

• According to Yale's undergraduate production program, the term prop gun can be used to describe non-firing weapons, rubber guns and toy guns. (The program site adds that prop weapons can be "capable of inflicting actual bodily harm" and need a to be handled with a level of safety protocol.)

• Prop guns can also refer to functional firearms that discharge blank ammunition, according to Sonoma State University's theatre arts department. These can produce a noise and can also pose a fire hazard, the site states.

How can a prop gun kill someone?

Functional firearms can be deadly, even when using blanks.

Such was the case with Hexum's accidental, self-inflicted gunshot to the head with a blank cartridge on the set of "Cover Up."

In an article for "The Conversation," filmmakers Christopher Gist and Sarah Mayberry explained how Hexum died.

"Instead of using a bullet, blanks use wads of paper, plastic, felt or cotton – this wadding ensures you get a certain level of flame out of the gun," they wrote.

The force of the wadding was enough to kill him.

The Actors' Equity Association has called blanks "extremely dangerous."

"Even though they do not fire bullets out of the gun barrel, they still have a powerful blast than can maim or kill."

On RJR Props and Set Dressing Services' website, a company that rents prop guns for use in film, television and video, it clearly states that its blank-firing guns are "dangerous and require a license or a registered armorer."

More on the incident:

• 'No one should ever be killed' by prop gun: Mishap surfaces Brandon Lee death

• Alec Baldwin discharged prop gun in incident that killed cinematographer, injured director

• Prop gun death at Alec Baldwin film 'Rust' isn't the first accident on a movie set

Blanks versus live rounds

To understand the difference between blank and live rounds, it's important to understand that, generally speaking, ammunition for firearms is made up of several parts: a casing, primer, powder and bullet.

The bullet specifically is the "projectile expelled from a gun," according to the National Rifle Association's glossary.

At its simplest definition, blanks lack a bullet. The NRA defines a blank cartridge as "a round loaded with blackpowder or a special smokeless powder but lacking a projectile."

Blanks can still use paper or plastic wadding to seal gunpowder into the cartridge, however, making them less dangerous than live rounds but still potentially harmful.

If propelled close enough to someone, such in the case with Hexum's death from a blank cartridge, a blank can cause injury or worse.

How could this happen?

According to the Actors' Equity Association, people handling props should "treat all guns as if they are loaded and deadly."

The group says to never point a firearm at anyone.

On set, the property master or armorer should train actors in the safe use of any firearm they must handle.

The weapons master is required to be on set whenever a weapon is being used. The Actors’ Equity Association’s guidelines state: “Before each use, make sure the gun has been test-fired off stage and then ask to test fire it yourself. Watch the prop master check the cylinders and barrel to be sure no foreign object or dummy bullet has become lodged inside.” Further, “all loading of firearms must be done by the property master, armorer or experienced persons working under their direct supervision.”

Kevin Williams, the prop department supervisor at the UCLA School of Theater, Film and Television, told NPR the Baldwin incident seems to be "one of these freak accidents."

"It is an extremely rare circumstance that anything like this happens. Especially nowadays when there are so many different procedures and policies in place," he said.

Why are guns used on sets?

When making a movie, Gist and Mayberry explained, choices in props are made to best match the characters and scene.

For a recent project they worked on, the team chose to film with real weapons but used only blanks in one scene. In every other scene, visual effects (VFX) will be added.

"The blanks were chosen because of the importance of the weapon to the storytelling in that scene," they wrote, but they added "many gun effects can be done well through VFX."

After the Baldwin incident, a Change.org petition was created titled "Hollywood: It’s time to ban the use of real firearms on film sets!"

The petition's description states: "We need to make sure this never happens again. There is no excuse for something like this to happen in the 21st century. Real guns are no longer needed on film production sets."

According to a press release, the petition was created by Bandar Albuliwi, a young director who graduated from the American Film Institute Conservatory, the same school Hutchins attended.

Other prop gun accidents: Jon-Erik Hexum, Brandon Lee

In addition to Hexum's 1984 death by blank firearm shooting and Bruce Lee's son's fatal shooting involving a prop gun, there have been other on-set accidents that have been the result of explosives and other stage weapons.

In 1982, three actors were killed and six helicopter passengers were injured on the set of "Twilight Zone" after special effects explosions caused a helicopter to crash.

Two of the actors who died were children.

The incident was responsible for new procedures and safety standards in the filmmaking industry after sparking years of civil and criminal action over what had happened.

Al Pacino accidentally burned his hand by holding the barrel of a gun that had been fired during production for 1983's "Scarface."

And Linda Hamilton suffered permanent hearing damage in one ear during filming of "Terminator 2: Judgment Day" in 1991 when she fired a gun inside an elevator without ear plugs.

Contributing: The Associated Press

This article originally appeared on USA TODAY: What is a prop gun? Alec Baldwin shooting incident raises questions.