EXCLUSIVE: A number of recent injuries on the set of Season 10 of ABC‘s 9-1-1 has put the production’s safety protocols under scrutiny again.

Deadline understands that four performers, including star Oliver Stark, have sustained stunt-related injuries to varying degrees in recent months. While the incidents do not seem to be connected, the unfortunate timing does highlight the challenges with making a stunt-heavy show like 9-1-1 on a broadcast network schedule.

A spokesperson for 20th Television, which produces the series, declined to comment for this story.

In late August, Stark broke his ankle while performing a stunt and required surgery. Sources close to production say that production continued in the wake of the incident and Stark has since returned to work. While reports of the injury surfaced online, the details of the incident have not yet been shared.

Sources tell Deadline that the stunt involved a firefighter swinging from a car over a set piece to the ladder truck. We understand that, during rehearsals, a stunt double sprained an ankle performing the same stunt and declined medical treatment, so no injury report was submitted to production.

On the 9-1-1 set, production sources say it is typical for stunts to be practiced first with heavyweight bags so the stunt coordinators and other crew members can better understand the necessary weight distribution, etc. Then, the set piece is rehearsed with stunt doubles to work out any issues before the actors come in for their own rehearsal.

In Stark’s case, we’re told the mechanics of the stunt were adjusted after the stunt double was injured. Sources indicate that, still, Stark rolled his ankle over another performer in the scene.

Two other injuries followed in subsequent weeks. In one incident, a stunt person injured their arm on a piece of the set that had jagged metal on it, requiring a hospital visit and stitches. Within the last two weeks, another stunt performer was sent to the hospital after a stunt gone wrong. Sources close to production say the hospital trip was “precautionary” after an “awkward landing” on a platform designed to simulate a ground collapse resulted in a broken rib and minor compressed lung. It’s unclear whether this performer has returned to work.

All SAG-AFTRA signatories, including 20th Television owner Disney, are required to follow certain on-set safety protocols. Stunt performers and coordinators are required to complete a general safety and injury prevention program in order to remain eligible for employment on union productions.

The standards and practices for set safety are developed by Contract Services’ industry wide safety committee. The general guidelines for stunts task production management with ensuring they “allow enough time for rehearsals, training, equipment preparations, and inspections,” per the company’s latest stunt safety bulletin. Contract Services also has more detailed guidelines for specific stunt work.

Typically, the stunt coordinator leads all stunt-related preparations including script review, planning, site selection, preparation, testing, rehearsal, modification, and recommendation of the qualified personnel and equipment to be utilized to perform the stunt. The first assistant director is responsible for holding an on-set safety meeting prior to any stunt work so all involved personnel can see a walk-through of the maneuver and discuss protocol in detail. Another safety meeting is required if there are any “substantive changes” to the stunt.

A concentration of injuries on a single season of television doesn’t necessarily indicate negligence, especially on a high-octane show like 9-1-1. However, it is ambitious for a series like 9-1-1 to pull off massive stunt sequences on a regular basis given the restraints of working within the relatively tight production schedule required of broadcast shows, making it more likely for problems to occur.

Two years ago, a crew member died from a cardiac event while driving home from set after the workday ballooned to 14 hours due to complications with a controlled burn that was being used for a stunt. Still, a production source told Deadline at the time that 9-1-1 was “one of the safest that I’ve ever worked on.”