If you saw a school bus engulfed in flames on the side of the road, you probably wouldn’t think the fire was caused by an air pollution regulation.

But in all likelihood, it was.

In 2008, the California Air Resources Board adopted the Statewide Truck and Bus Rule, which said diesel engines manufactured before 2010 could not be operated on state roads unless they were outfitted with a filter — at a cost of up to $15,000 per vehicle — to reduce the amount of fine particles released into the air.

The Alliance for California Business has been collecting data on incidents of fires in the engine compartments of trucks and buses, including school buses, equipped with diesel particulate filters. The evidence shows that the filters are causing truck and bus engines to burst into flames.

In 2013, the alliance filed a lawsuit against CARB seeking to have the Truck and Bus Rule thrown out. Truck owners, operators, mechanics and an automotive engineering expert explained how the diesel particulate filters damaged engines by exposing them to high heat and backpressure, leading to dangerous fires. Late last year, CARB’s lawyers prevailed by assuring the judge that there was no safety problem.

But now CARB is proposing a new regulation for the sale of aftermarket parts to repair the costly filters, and the agency has just released documents acknowledging what the alliance has been saying all along: Even when working as designed, the filters generate excessive heat, damaging both the filters and the engines, and sometimes causing explosive fires.

Last March, Orange County school bus driver Lisa Sherrill was transporting three dozen seventh- and eighth-graders to Rancho Santa Margarita Intermediate School when she saw smoke and flames coming from the engine compartment. Sherrill managed to get the children safely off the bus, which was fully engulfed in flames by the time firefighters arrived on the scene.

A few months later, a tour bus carrying 54 children caught fire on Highway 17 south of San Jose.

The Alliance says the number of bus fires throughout California is increasing and called on CARB to suspend the diesel particulate filter requirement “before one of these incidents turns into unimaginable tragedy.”

It doesn’t help that the members of the Air Resources Board were tricked into voting for the Truck and Bus Rule. They were shown a statistical analysis which concluded that 9,400 premature deaths in California would be prevented by further reducing “fine particulate” air pollution from diesel engines. But then it turned out that the lead author of that study, CARB staffer Hien Tran, had purchased his Ph.D. in statistics from a diploma mill for $1,000. CARB chair Mary Nichols knew about the deception, but did not tell the board before the vote.

According to other studies — by scientists with genuine doctorate degrees — there are no premature deaths caused by fine particulate air pollution in California.

Secrecy surrounds the data used by government officials to justify the high cost of each new wave of air quality restrictions. Federal and state regulators come up with “premature death” numbers by interpreting two studies from the 1990s, but the underlying data from those studies has never been made available to independent scientists or even to the EPA itself. A proposed federal law to prohibit the EPA from making regulations based on “secret science” passed the House last year but stalled in the Senate.

The bill, S 544, deserves a vote. With a little more transparency, we could preserve the clean-air regulations that really clean the air and get rid of the ones that just burn us.