'Unknown odor' on Alaska Airlines plane sends 2 flight attendants to hospital

An Alaska Airlines flight was canceled Monday night after two flight attendants became ill. The carrier said the cause was likely an "unknown odor" in the rear of the plane.

Flight ASA 828, which was to depart from Honolulu at 11:45 p.m. to Anchorage, was in its boarding process when two female crew members reported feeling sick.

At around 11:15 p.m., Honolulu Emergency Medical Services treated and transported them to the emergency room in "serious condition," a spokesperson for Honolulu EMS told USA TODAY.

"This incident was properly reported to the appropriate agencies for further action," Alaska said.

Cruising Altitude: Yes, you could inhale toxic fumes during your flight

The two crew members have since been medically cleared to resume flying.

Nearly all airplanes have ventilation systems designed to bring fresh air through the engines without using a filter. Sometimes toxic fumes from other parts of the plane can get sucked into the main cabin and, since there's no filter, contaminate the air. Exposure to toxic fumes can cause people to feel dizzy, nauseous, or experience headaches or cramping.

Research has found toxic fume incidents on planes to be rare, happening between 0.09 and 3.9 per every 1,000 flights. That's about two to three incidents per day in the U.S.

Since flight attendants spend so much time in aircraft cabins, they're most at risk of toxic fume exposure.

Kathleen Wong is a travel reporter for USA TODAY based in Hawaii. You can reach her at kwong@usatoday.com.

This article originally appeared on USA TODAY: 'Unknown odor' on Alaska Airlines plane sends crew members to hospital