Twenty students and their physical education teacher fell ill yesterday after inhaling pesticides that spread into a Tuen Mun school. The pesticides were being sprayed nearby by two hygiene workers during an anti-mosquito operation. Principal Lam Chi-hung, of the San Wui Commercial Society Secondary School, said the Food and Environmental Hygiene Department had been inconsiderate when it carried out the operation. He said he had lodged a complaint with the department. The incident happened just after 11am when 28 Form Two students were attending a physical education class at an outdoor basketball court at the school on Leung King Estate. Mr Lam said two workers from the department were spraying pesticides in bushes just outside the school railings and only metres away from the students. Their PE teacher ran to stop the work but the spray spread into the school. Nine boys and the 40-year-old teacher were taken to Tuen Mun Hospital and medical staff treated another 11 students at the school. Last night, a 14-year-old boy remained in hospital under observation. The others were discharged. Mr Lam said: 'The incident could have been avoided if they had alerted us and we could have arranged the physical-education class in our indoor hall. 'I am very dissatisfied over the incident. It appears that they had not considered the impact of spraying pesticide to nearby residents and schools.' A spokesman said the department had reminded workers to follow guidelines and alert the public to take precautionary measures if necessary.