An empirical study on the wake around a squatting worker in a confined space.

Objectives: When an air current flows from behind a worker, the contaminant level in the breathing zone may increase due to the wake around the worker. Researchers have been investigating about this wake, and much knowledge has been provided about the wake that appears around a standing worker. However, the wake around a squatting worker has not been addressed. This study aimed to describe the wake in front of a worker squatting in a confined space by using a model worker and a chamber and investigate the conditions in which this wake develops easily.

Methods: A mannequin was employed as a model worker and was placed in the chamber to simulate a squatting worker in a confined space. Then, air was sent from behind under various conditions with a fan, and the wake was observed.

Results: A wake appeared when smoke was emitted at 0-0.1 m from the point just below the breathing zone, and most of the wake region was in the range between the point just below the model worker's breathing zone and body. A wake did not appear when a fan of 0.15 m in diameter was used. The flow rate and velocity of the airflow were almost irrelevant with respect to wake development.

Conclusions: The following are recommended based on the results of the present study. i) The distance between a source of contaminants and the point just below the breathing zone should be more than 0.2 m. ii) An air duct with a cross-section of less than 0.02 m(2) is desirable to avoid producing a wake.