LOS ANGELES —

Elon Musk knows his audience. He just sold tens of thousands of hats emblazoned with the name of his Boring Co. tunnel business, then followed up by slapping his brand on something far less practical: flamethrowers.

The Los Angeles entrepreneur — who also leads SpaceX and Tesla Inc. and has a flair for showmanship — said Monday that his tunneling firm had pre-sold 10,000 Boring Co.-branded flamethrowers since Saturday, pulling in $5 million.

Musk’s fans flocked to his side project even as one of his main ventures founders. Tesla received many preorders for its new Model 3 electric sedans, but it has yet to ramp up output of the cars as promised. Musk has said Tesla is in “production hell.”

His brand has stayed strong. Musk’s devoted fans snapped up 50,000 Boring Co. hats at $20 each and the flamethrowers — which Musk promised to start shipping this spring — for $500 apiece. Musk also said Monday that he’d sold about 3,000 admittedly overpriced fire extinguishers ($30 each).

Flamethrowers have nothing to do with Hawthorne-based Boring Co.’s stated mission of creating tunnels as a way to reduce surface-level street traffic. Their buyers probably don’t need the flamethrowers to, say, clear brush from large tracts of land or to melt snow and ice. On its website, Boring Co. describes the fire-spouting devices as “guaranteed to liven up any party!” Musk tweeted over the weekend that a flamethrower was a “super terrible idea” and encouraged his followers not to buy one — “unless you like fun.”

California Assemblyman Miguel Santiago (D-Los Angeles) wasn’t smiling. He said Monday he was worried the sale of the flamethrowers could be a public health hazard.

“We’ve just gone through some catastrophic fires in California,” he said. “It’s a bad joke.”

Such devices have also been used to devastating effect in war. In 1983, 115 nations — including the United States — agreed to prohibit attacks on civilians with “incendiary weapons,” which includes flamethrowers.

The devices do have some peaceful, practical uses.

Farmers and ranchers have bought flamethrowers from Cleveland, Ohio-based Throwflame to clear their fields at the end of growing seasons, and firefighters have used the devices to do controlled burns as they seek to contain the spread of wildfires, Throwflame Chief Executive Quinn Whitehead said.

Phoenix-based Ion Productions Team said its flamethrowers can be used to clear snow and ice, or to incinerate weeds on large lots of land. Customers are about evenly split between those who use the flamethrower for fun and those that use it for work, especially on farms in rural areas, CEO Chris Byars said.

In California, there are some restrictions. State health and safety codes mandate that to use flamethrowing devices with a range of at least 10 feet, a person must have a permit or be part of a firefighting agency.

A Boring Co. spokesman said the flamethrowers on pre-sale have a range of less than 10 feet, so no such permits are needed. A short video on the company’s website shows the devices spitting a few feet of fire.

Flamethrower manufacturers say Musk’s foray into flamethrowers has led to more interest in their own products.

Whitehead said Throwflame customers have placed “quite a few” orders since Musk first began tweeting about his flamethrower promotion.