Objective To collect evidences of air ventilation system pollution of air-conditioned carriages and to provide scientific basis and reasonable proposals for disease prevention.
Methods Three models of representative air-conditioned carriages (25G, 25T and CRH-5) were selected, and each was monitored at 4 sampling points including hard seat, hard berth, soft berth and dining-car in April, May and June of 2011. The monitoring indices of air supply system included temperature, humidity, in halable particles (PM10), air exchange flow and the total colony forming units (CFU) of bacteria, fungi and β-type hemolytic streptococcus. The monitoring indices of air ventilation ducts included the amount of dust particles and the total CFU of bacteria and fungi. The monitoring index of condensed water was Legionella pneumophila.
Results No Legionella pneumophila was found in the condensed water of air ventilation system of 25G and 25T carriages. The average air exchange flow of 25G, 25T and CRH-5 carriages were (49.1& #177;10.3), (41.5& #177;18.1) and (52.4& #177;12.3) m3/(h& #183;p) respectively. In the air supply system, the average humidity were (40.1& #177;1.5)%, (29.4& #177;7.3)% and (42.1& #177;4.5)% respectively; the average CFU of bacteria were (603.7& #177;124.0), (643.3& #177;331.3) and (256.5& #177;67.7) cfu/m3 respectively; the average CFU of fungi were (148.7& #177;39.7), (216.8& #177;227.6) and 0.0 cfu/m3 respectively; the average CFU of β-type hemolytic streptococcus were (7.3& #177;5.6), 0.0 and 0.0 cfu/m3 respectively. In the air ventilation duct, the average amount of dust particles were (8.5& #177;1.5), (9.2& #177;8.7) and (5.0& #177;0.5) g/m2 respectively. There was a significant difference in humidity among selected models (F=4.685 6, P=0.011 5), but no significant difference was found in other monitoring indices.
Conclusion The problems of the amount of dust particles in air ventilation ducts and the total CFU of bacteria, fungi and β-type hemolytic streptococcus in air supply system of selected models exist in varying degrees. Regular cleaning and disinfection, and air purifier installment if allowed, should be undertaken to control microbes from growing in the air ventilation system of air-conditioned carriages.
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