Abstract for Poster 49

 

 

Designing Ducting System for a Manufacturing Industry Based on Ventilation and Chemical Measurements

J. Lu
National Institutes of Health, University of the Philippines, Manila, Philippines

Introduction

This study was conducted in a manufacturing industry in the Philippines that uses toxic chemicals such as trichloroethylene, sulfuric acid, ethylene chloride, acetone and alcohols. The industry employs about a thousand workers, and the recent medical record shows an increasing number of workers having eye and skin irritation. Results showed that there was a relationship between eye and skin irritation and increases in solvent concentration, lower capture velocities, higher ambient temperature and lower ventilation readings in workstations. To allow better exposure controls to be designed, baseline measurement was done of ventilation and chemical concentration for the work processes. Results

Results are presented in Table 1 and Table 2.

Based on the results, the capture velocities were negligible and thus the ducting system was not effective. Some solvents exceeded the threshold limit value. These caused the eye and skin irritation at work.

Recommendations

For the 1.67 Area, it is suggested that an additional round duct be extended to where the worker is performing her work. With inclusion of a non-corrosive plastic curtain to enclose the work area, only the hands of the worker will be placed inside. By doing this, negative pressure is built inside the curtain and positive pressure outside. This will push the toxic vapours into the ducting system. For another ducting system that connects to the 1.67 area as shown below, the slot velocity should be a minimum of 2000 fpm as recommended. The air velocity in the measurement was far below this recommended capacity, and this can be improved by improving motor capacity or increasing fan capacity. For the trichloroethylene, the slot should extend over the tank as far as possible to contain the vapour.

 

Table 2. Baseline measurements of chemical concentration for different work areas
WorkArea	Sodium Hydroxide (mg/m3)	Trichloro-ethylene (mg/m3)	Isopropyl Alcohol (mg/m3)
Area A (Exhaust Area)	10.0	1.6	1.0
Area B (Exhaust)	6.4	Below 1	163.5
Area C (Supply)	15.9	0.3	0.3

 

For any hood design, the hood angulation from the duct should be a minimum of 45 degrees. The height of the hood from work process should not be greater than 12 inches to increase capture velocity. It is recommended that flexible type of hood adjustment be incorporated. When there is no production, the hood can be put up, and when there is production, the hood can be lowered down. Lower the hood to the work process to a maximum of 12 inches or 1 foot to enhance the capture capacity of the ducting system. A flexible and adjustable hood is recommended that can be lowered and raised. The cleaning of the ducts should be done regularly. Wash-down facilities in the hood and ducts are recommended to clean the hoods and ducts. Avoid sharp turns in the design of the ducting system. This will generate turbulence. Lubricate the fan regularly. The exhaust discharge must terminate out-of-doors, preferably using a vertical discharge cap that extends well above the roof eddy zone.

 

Content last modified: 24 May 2005