A man rides an electric rental scooter along a city street in San Diego, Calif., on Sept. 4. (Mike Blake/Reuters) (MIKE BLAKE/Reuters)

A 24-year-old Dallas man who died after falling off a Lime electric scooter was killed by blunt force injuries to his head, county officials said Thursday, likely making him the first person to die in an accident involving the electric mobility devices that have swept across the nation this year.

The death of Jacoby Stoneking has been ruled an accident, the Dallas County Medical Examiner’s Office told The Washington Post before releasing the information publicly. Police said Stoneking was riding a Lime scooter home from a restaurant where he works when the accident occurred. He was found unconscious and badly injured in the early morning hours of Sept. 1, several hundred yards from a scooter that was broken in half. He was not wearing a helmet, according to a person familiar with the matter who spoke on condition of anonymity to talk freely about the investigation.

The determination by Dallas officials emerged just after California Gov. Jerry Brown (D) signed a bill Wednesday that makes it legal for adults to ride electric scooters without a helmet. The new law also grants cities in California the authority to let scooters operate on streets with speeds limits up to 35 mph, a 10 mph increase.

The three largest e-scooter companies, Lime, Bird, and Skip, said they were unaware of any other fatal accidents involving their devices. When asked for comment about the passage of the California bill in light of the e-scooter death in Dallas, Ali Bay, deputy press secretary for Gov. Brown, simply responded in an e-mail: “The Governor’s action speaks for itself.”

Lime has pledged to launch an investigation into Stoneking’s death.

In a statement Thursday, Lime said it so far has found no evidence of a scooter malfunction. The company also said, “Our thoughts and sympathies are with the family and loved ones of the victim. We are working tirelessly with local authorities in support of their ongoing investigation. We have and will continue to work with them in a transparent manner.”

Financial analysts say Lime may be worth more than $1 billion in market value after receiving $335 million in financing that included a major investment from Uber. In an interview with The Washington Post earlier this year, Uber’s chief executive Dara Khoshrowshahi spoke of the critical role e-scooters and bike-sharing could have in his company’s efforts to transform urban transportation.

Khoshrowshahi has also taken pains to rehabilitate Uber’s image as a grow-at-all-costs company. When an Uber self-driving car struck and killed an Arizona woman in March, Khoshrowshahi quickly froze the company’s autonomous driving program until it could be deemed safe.

When told about the Lime fatality, Uber said in a statement: “Customer safety is essential to Uber, whether for bikes, scooters or cars. As we continue working through our scooter product and Lime integration, we’re keeping safety top of mind.”

The three e-scooter companies have aggressively expanded nationally, and some analysts estimate as many as 65,000 scooters are now on streets across the country. The start-ups have also launched services overseas.

But almost as soon as the scooters arrived in towns and cities, severe injuries have followed.

Emergency room doctors in a dozen cities told The Post that they are seeing a spike in scooter accidents. In seven cities, those physicians are regularly seeing “severe” injuries — including head traumas — that were sustained from scooters malfunctioning or flipping over on uneven surfaces as well as riders being hit by cars or colliding with pedestrians.

“An electric scooter is pretty much a moped, just a little slower,” said Dr. Sam Torbati, co-chair and medical director of the Ruth and Harry Roman Emergency Department at Cedars-Sinai in Los Angeles. “People seem to feel safe since it looks like a recreational tool, but it comes with potential for serious injury.”

Torbati said it will take another year for the hospital to collect enough data to make a proper risk assessment for electric scooters, but he parroted a message repeated by every doctor The Post interviewed: Wear a helmet.

“It makes me real anxious when I see someone with ear buds and a cup of coffee riding without a helmet on the sidewalk,” he added. “The public is excited for this fun new form of transportation, but the injuries we’re seeing suggest they’re not aware of the risks involved they could get seriously injured.”

Dr. Christopher Michael Ziebell, the medical director for Dell Seton Emergency Department in Austin Tex., said his staff has treated nine “severe traumas” stemming from electric scooters since the devices arrived in Austin in April.

For whatever reason, he said, scooter riders seem to feel “invincible” as they weave through traffic and sidewalks.

But their brains are especially vulnerable during accidents, and a severe head injury can result, Ziebell said.

“A severe head injury is not a simple concussion or a skull fracture,” he said. “It’s actually bleeding inside the skull cavity in or around the brain that results in damage to parts of the brain that may sometimes be permanent. It requires significant rehabilitation and prolonged hospitalization to treat.”

Scooter companies have repeatedly maintained that safety is a top priority. They say their apps and labels on the scooters contain basic safety information, as well as training instructions. Bird requires users to upload a driver’s license and confirm they’re at least 18 years old.

Lime, Bird and Skip have programs that give helmets to riders who request them, and Lime notes that riders must go through an “in-app tutorial” on helmet safety to unlock one of the company’s scooters for the first time.