The paper deals with a three dimensional modelling of an experimental device realized in the Department of "Fisica Tecnica" of the University of Rome "La Sapienza" in cooperation with the Italian National Council of Researchers (CNR) in order to investigate the performances of shutter type air curtains as a dynamic barrier against the diffusion of fumes or airborne toxic substances.

This paper presents the results of the numerical simulation on the ventilation efficiency and the residual age of air by using CFD in the underground car park in which the field measurement was conducted as shown in a previous paper. The agreement between the CFD result and the measurement one was observed at most of the measuring points. The detailed distribution of local air change effectiveness was examined with the results from CPD in this paper.

This paper presents the field experiments on the ventilation efficiency in an underground car park where high velocity fan-diffuser units were installed as shown in Photo 1. The concentration of SF6 were measured as tracer gas under the step up condition and the step down condition, and the ventilation efficiency such as the age of air were calculated from the rising curve and the falling curve of the SF6 concentration in the underground car park. The ventilation efficiencies of two cases were compared, i.e.

The rotating vane anemometer is an instrument that is widely used in the field by maintenance engineers and inspectors. The anemometer consists of a vane that is held at right angles to an airflow. In modem instruments the speed of rotation of the vane is sensed and measured electronically and the air speed, which is a function of the speed of rotation of the vane, is indicated on a meter.

Occupational hygiene conditions were examined in a welding shop after repairing the air-handling unit. Good indoor air quality was achieved with the new replacement ventilation system. The airborne dust concentrations varied from the detection limit of 0.1 mg/m3 to 0.8 mg/m3 at the stationary sites. Even the breathing zone concentrations of the welders remained below or equal to 2.1 mg/m3. The concentrations of carbon monoxide did not exceed the level of 1 cm3/m3.