On Jan. 14, a Delta plane departing Los Angeles for Shanghai requested an emergency landing shortly after takeoff, citing engine problems. The pilot of Delta Flight 89 told air traffic controllers that dumping fuel was unnecessary, but then the Boeing 777-200 proceeded to do just that at low altitude over a densely populated area, drizzling students and teachers at elementary schools and playgrounds below.

Yesterday, four area teachers filed a lawsuit against Delta in Los Angeles Superior Court. That followed air quality regulators in Southern California hitting the company (pdf) with a formal notice of violation, and the Federal Aviation Administration announcing that it will “thoroughly investigate” the incident.

The teachers argue that Delta was negligent in allowing the plane to depart in the first place, and said that the pilots failed to follow protocol. Their attorney noted “they also suffered severe emotional distress from the knowledge that they had involuntarily ingested toxins,” adding that young children screamed and cried.

Delta has not yet commented on the suit, though it said in a Jan. 15 statement that it had dispatched cleaning crews to the affected schools after the incident and that “residual health effects are not expected.” The Los Angeles County Fire Department said that dozens of children and adults suffered minor injuries, but none needed hospitalization.

It’s not unheard of for planes to need to turn around for emergency landings after takeoff, and to dump fuel to achieve a safe landing weight. But usually air traffic controllers direct pilots to dump fuel over less populated designated areas and at higher altitudes, allowing the fuel to properly atomize. David Soucie, a CNN aviation safety analyst, noted that the pilot said the engine was under control, so he could have taken the plane over the ocean to dump fuel or burn it off.

One of the teachers noted that her fifth-grade students thought the jet fuel was rain, “only to have noxious liquid then overwhelm [their] eyes, mouths, noses, lungs and skin.”