Experimental investigation of the concept of a 'breathing zone' using a mannequin exposed to a point source of inertial/sedimenting particles emitted with momentum.

An inhaling mannequin, CALTOOL, was used in a specially ventilated room to compare the concentrations inhaled with those sampled by samplers mounted across the breathing zone. The CALTOOL is made from metal sheets and consists of a cylindrical torso (42 x 24 x 54 cm) with a circular cylinder as head. A circular nozzle simulates the mouth. This nozzle is part of a cassette that holds a filter. The inhalation rate is not periodic but kept constant at nominally 20 l min(-1). The CALTOOL was placed in a horizontal air stream ( approximately 10 cm s(-1)) either facing or back to the wind. In front of the lower chest of the CALTOOL, a particle source was mounted which emitted particles with a momentum directed upwards at an angle of 45 degrees towards the CALTOOL. Five monodisperse aluminium oxide powders were used as test aerosols. The mass median aerodynamic diameters of the test aerosols ranged approximately 10 to 95 mum. Six conically shaped aerosol samplers were mounted horizontally and over the breathing zone of the CALTOOL, one on each shoulder, three across the upper torso, and one at the lower torso centre. Four to six runs per test aerosol and CALTOOL orientation in the airflow were conducted. The samples were analysed gravimetrically. The concentration ratio aerosol sampler to the CALTOOL cassette was determined for the investigated mounting positions. The results showed that when the CALTOOL was exposed to particles emitted with momentum from a point source in front of the lower chest, the variation in concentration over the breathing zone was large. The ratio of the concentration sampled by an aerosol sampler mounted somewhere within the breathing zone to the CALTOOL cassette concentration, would, for specific particle sizes, easily differ by a factor of 3, but may extend up to 10-100, depending on the particular conditions. The basic concept of a breathing zone consisting of a hemisphere of radius 25-30 cm is therefore not well suited for workers handling a point source emitting large particles. For such sampling situations, it is suggested that the radius of the breathing zone is reduced to 10 cm, which may be achieved by a head-mounted sampler.