Narrative:

At approximately 500 ft AGL on a visual approach the flight attendants rang us repeatedly from the cabin. I briefly considered whether we should go around, but decided to land and then talk to them. The first officer continued to monitor my approach and landing while the flight attendants rang us with increasing urgency. During the landing rollout, the flight attendants began to bang on the cockpit door. The first officer then picked up the handset. He told me that they were 'choking' due to some kind of 'gas' in the cabin. He then declared an emergency with tower and told them to expect an evacuate/evacuation. I quickly stopped the plane on a highspd taxiway, set the brake, turned off both air conditioning packs, and with the first officer's help, configured the plane for evacuate/evacuation. I then had the first officer open the cockpit door. At that point I could sense no 'gas.' I had the flight attendants open the forward galley service door and the main cabin door. The flight attendants said the gas was dissipating in the cabin. Because of this, I had the passenger evacuate/evacuation down the forward stairs rather than risk injury on the slides. This was done in an orderly manner. Afterwards, the plane was inspected by a policeman and fire fighters. They concluded that someone had released pepper spray into the cabin. (Company mechanics found nothing wrong with the plane.) unfortunately neither the culprit or the pepper spray device was discovered. Later I learned that carrying pepper spray is quite prevalent. Also, there have been other instances of accidental or intentional release in public places (including on another aircraft). These devices are quite small and must be difficult for security to screen. We were quite fortunate that only 2 passenger had to be treated for eye and throat irritation. (I hate to think what would have happened had we gone around!) I am concerned that this will happen again with more serious consequences.

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Original NASA ASRS Text

Title: DC9 IS EVACED WHEN A PAX RELEASES PEPPER SPRAY EITHER INTENTIONALLY OR UNINTENTIONALLY.

Narrative: AT APPROX 500 FT AGL ON A VISUAL APCH THE FLT ATTENDANTS RANG US REPEATEDLY FROM THE CABIN. I BRIEFLY CONSIDERED WHETHER WE SHOULD GAR, BUT DECIDED TO LAND AND THEN TALK TO THEM. THE FO CONTINUED TO MONITOR MY APCH AND LNDG WHILE THE FLT ATTENDANTS RANG US WITH INCREASING URGENCY. DURING THE LNDG ROLLOUT, THE FLT ATTENDANTS BEGAN TO BANG ON THE COCKPIT DOOR. THE FO THEN PICKED UP THE HANDSET. HE TOLD ME THAT THEY WERE 'CHOKING' DUE TO SOME KIND OF 'GAS' IN THE CABIN. HE THEN DECLARED AN EMER WITH TWR AND TOLD THEM TO EXPECT AN EVAC. I QUICKLY STOPPED THE PLANE ON A HIGHSPD TXWY, SET THE BRAKE, TURNED OFF BOTH AIR CONDITIONING PACKS, AND WITH THE FO'S HELP, CONFIGURED THE PLANE FOR EVAC. I THEN HAD THE FO OPEN THE COCKPIT DOOR. AT THAT POINT I COULD SENSE NO 'GAS.' I HAD THE FLT ATTENDANTS OPEN THE FORWARD GALLEY SVC DOOR AND THE MAIN CABIN DOOR. THE FLT ATTENDANTS SAID THE GAS WAS DISSIPATING IN THE CABIN. BECAUSE OF THIS, I HAD THE PAX EVAC DOWN THE FORWARD STAIRS RATHER THAN RISK INJURY ON THE SLIDES. THIS WAS DONE IN AN ORDERLY MANNER. AFTERWARDS, THE PLANE WAS INSPECTED BY A POLICEMAN AND FIRE FIGHTERS. THEY CONCLUDED THAT SOMEONE HAD RELEASED PEPPER SPRAY INTO THE CABIN. (COMPANY MECHS FOUND NOTHING WRONG WITH THE PLANE.) UNFORTUNATELY NEITHER THE CULPRIT OR THE PEPPER SPRAY DEVICE WAS DISCOVERED. LATER I LEARNED THAT CARRYING PEPPER SPRAY IS QUITE PREVALENT. ALSO, THERE HAVE BEEN OTHER INSTANCES OF ACCIDENTAL OR INTENTIONAL RELEASE IN PUBLIC PLACES (INCLUDING ON ANOTHER ACFT). THESE DEVICES ARE QUITE SMALL AND MUST BE DIFFICULT FOR SECURITY TO SCREEN. WE WERE QUITE FORTUNATE THAT ONLY 2 PAX HAD TO BE TREATED FOR EYE AND THROAT IRRITATION. (I HATE TO THINK WHAT WOULD HAVE HAPPENED HAD WE GONE AROUND!) I AM CONCERNED THAT THIS WILL HAPPEN AGAIN WITH MORE SERIOUS CONSEQUENCES.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.