LOS ANGELES - Hundreds of law enforcement officers on Friday raided Southern California auto parts shops and other businesses suspected of illegally selling nitrous oxide for use as a recreational drug, in what federal authorities said was the nation's largest such raid ever.

Authorities served search warrants on 17 businesses and nine delivery vehicles during the simultaneous raids in Los Angeles, Orange and Riverside counties.

Edward Valencia, 51, Federico Valencia, 58, and Rose Marie Cuellar, 20, were arrested on misdemeanor charges of misbranding a drug in violation of the federal Food, Drug, and Cosmetic Act. The Valencia brothers work at Victor Welding Supply in South Los Angeles, and Cuellar is an employee of LA Rush, an auto parts store.

"I'm innocent. I haven't done anything wrong," Federico Valencia said as he was led out of his shop in handcuffs. "We only sell gases for cars."

It was the second time the shop had been raided. In 2009, authorities spoke with the Valencia brothers and owner William Victor about their sales of nitrous oxide and its popular use as a party drug, according to a federal affidavit.

Victor, 65, also was named in an arrest warrant and was being sought by authorities Friday.

The raids were the result of a year-and-a-half-long joint investigation dubbed "No Laughing Matter" by the Food and Drug Administration's Office of Criminal Investigations and the Los Angeles County Sheriff's Department.

During the operation, federal agents seized 367 tanks or 36,000 pounds of nitrous oxide with a street value of $20 million, said Andre Birotte Jr., U.S. attorney for the Central District of California.

"Our investigation has revealed and uncovered evidence that many of these shops don't contain any auto supplies at all, just tanks of nitrous oxide," Birotte said.

The FDA has recently focused on the illegal use of nitrous oxide, and this was its largest case to date, said special agent Lisa Hartsell. Though nitrous oxide, also known as "laughing gas" or "nos," has long been a rave phenomenon, it has recently grown into more mainstream use, propelled by the ease of social media to reach young people and spread the word.

"This is a very cheap drug, can be had very easily, it is not a controlled substance, so your big members of the law enforcement community don't have the ability to control it," Hartsell said.

The gas is legally used by dentists for anesthesia, to pressurize whipped cream canisters and to speed up race cars. But authorities say its illegal use has spurred fatal car accidents, rapes and teen deaths - all in the name of a temporary high.

"We believe these individuals are selling this nitrous oxide knowing full well that it's not going to be used to accelerate a race car or for a dental office, it's being used for the party scene," Birotte said.

If ingested at high levels, nitrous oxide can cause death from lack of oxygen; it can also lead to spasms, convulsions and other health problems. Nitrous oxide is also considered a greenhouse gas and is 310 times more dangerous to the Earth's ozone layer than carbon dioxide, said Joseph Johns, chief of the U.S. attorney's environmental crimes section.

"The amount of gas that was taken off the streets today, is equivalent to one year's worth of carbon dioxide emissions from a small petroleum refinery in the heart of Los Angeles," Johns said. He said the investigation is ongoing.

"These (raids) are the initial baby steps," and more charges would likely be filed in the next weeks, Johns said.

Los Angeles County sheriff's officials have zeroed in on the recreational use of nitrous oxide since September, cracking down on more than 350 illegal parties, spokesman Mike Parker said Thursday.

The operations are part of a new team set up by the Sheriff's Department over the last six months to monitor social media around the clock. The team has found many public posts that target teens and advertise alcohol and illegal drugs such as nitrous oxide.

"They're doing the social media equivalent of standing outside the front doors of a high school at 3 o'clock as school lets out with a megaphone announcing that there'll be drugs, noz and alcohol for children, and then handing out fliers to all the kids that are interested," Parker said.

These parties can be lucrative for those provisioning them. Sheriff's deputies have been tracking one distributor who is making more than $60,000 a month in the bulk sale of nitrous oxide, said Sgt. Glenn Walsh, who works in the Sheriff's Department's narcotics bureau.

Hartsell said the drugs have also spurred armed robberies as gangs steal tanks from each other.

Part of the problem for law enforcement officers going after the illegal use of nitrous oxide is that its distribution or use as a recreational drug is only a misdemeanor, officials said.

Sheriff's Lt. Rod Armalin said the department is working on legislation to increase the penalties.

Nitrous oxide isn't the only dangerous substance teens are turning to for a quick and cheap high. On Monday, a 14-year-old Los Angeles honors student died after inhaling computer keyboard dust cleaner, apparently to get high. Aria Doherty's sister found her in bed with a can of compressed air cleaning product attached to her mouth.