Flights from Chiang Mai and Mae Hong Song were suspended on Monday due to haze from a forest fire Mae Hong Song which reduced visibility to 1.5 km. The amount of small particulate matter up to 10 microns in diameter (PM10) in 24 hours peaked at 156 micrograms per cubic metre of air, with an average of 138 micrograms, compared to Sunday's peak of 180. The safe level of PM10 is 120 micrograms, which, if exceeded, can pose health risks. Bangkok Airways cancelled its two morning flights between Chiang Mai and Mae Hong Son but the evening ones operated as usual. All four Kan Air flights were cancelled until today. Kan Air brought a 12-seat aircraft to transport stranded passengers in one trip yesterday. It is suspected that the haze stemmed from villagers taking the opportunity to do outdoor burning before the 61-day ban is imposed from March 1 - Wednesday - until April 30. Muang Mae Hong Son district chief Pisit Boonkij-anan urged residents and community leaders to refrain from burning. Provincial natural resource and environment office head Somsak Sappakosolkul said his office would arrange a helicopter survey of the forest fire situation to assess and find solutions to the problem. The Pollution Control Department urged related agencies to help prevent outdoor burning and advised small children, elderly people and those suffering from chronic respiratory illness to avoid staying outdoors, and to seek medical attention if they become sick. Public Health permanent secretary Dr Sopon Mekthon said he had instructed the Northern Region's public health office to distribute face-masks to affected residents. They were also ordered to send teams to do health checks for at-risk groups in the affected area, and to have district hospitals modify a conference hall or large room as a "clean area" with air-filtered conditioners to support affected patients.