抄録
It is well known that most dust in the lecture room is chalk dust. Dust concentrations were measured at intervals of 3 minutes on a horizontal plane and a vertical plane, after wiping the blackboard for 20 seconds on which many letters were written. Also particle size distributions were measured. The state of dispersing and floating dust in the lecture room can therefore be determined. The results are discussed as a guide to the measurement of dust described in “Requirements for a healthful school environment”.
The following results were obtained:
1) The dust environment in the lecture room is separated into three sections by dust isoconcentration curves, that is, a position less than 2.5m distant from the blackboard shows the highest dust concentration, and a position farther than 5.0m distant from the blackboard shows the lowest dust concentration.
2) Each dust concentration appears similar to a damped oscillation decreasing during 7 to 8 minutes after wiping the blackboard. After this, the dust concentration does not change but shows the floating dust concentration.
3) The dust concentration at 10 minutes after wiping the blackboard is almost the same at all heights, but the farther the distance from the blackboard, the lower the concentration of dust.
4) All particle sizes of chalk dust are shown to be below 7.0μ diameter (by 1-b) and the greater part are below 5.0μ diameter (by 1-b). The proportion of particles below 0.9μ diameter (by 1-b) shows no change at distances farther than 4 to 5m from the blackboard.
5) In order to evaluate correctly the dust environment in the lecture room, dust concentrations should be measured at 10 minutes after wiping the blackboard. Measurements should be taken at more than three positions on the center line of the lecture room, including the teacher's desk, 2.5 to 5.0m distant and more than 5.0m from the blackboard.
