VENTILATION
The survey of existing arrangements
revealed that the down-flow booths did not meet current design guidelines. The position of the extract points on the rear wall of the booth meant that uniform laminar airflow could not be achieved and this presented an opportunity to reduce production hazards associated with filling the flasks with methanol, fitting stirrers and venting tubes to the flask and loading the oven by re-engineering the fume management system. The survey also provided an opportunity to examine how workflow could be improved by the architectural design of the refurbishment. The previous layout involved filling flasks with methanol on the front edge of the booth, where controlled air flow could not be maintained. Fitting and removing stirrers took place above the flat surface supporting the flasks, creating the potential for the vertical down-flow of fresh air to bounce up off the flat surfaces and create an area of turbulent air. The horizontal surface where the preparation was placed ready for loading into the oven was another potential area of turbulent air in the operator breathing zone.
An iterative process Working closely with the client, including the operatives using the booths and fume cupboards, the challenges of improving fume control and reducing manual handling of the methanol required in the production process was considered. Improvements to the flask filling requirements were addressed by external methanol storage and a piped distribution system, which allows operatives in the refurbished facility to fill a flask by simply opening and closing a spring loaded valve. This not only avoids the need for methanol to be brought into the building in drums, but also means that the operator can work in a position where fumes are not in close proximity to his or her breathing zone because he or she no longer needs to lean over the flask. The design of the booth was more of
an iterative process, with several designs considered in order to achieve the initial design intention of separating the operator from the process as much as possible. A restricted access barrier (RAB) combined with automated flask filling and emptying would have achieved this, but this option was rejected due to the work flow implications of a restricted access arrangement. Incorporating the whole of the purification process into a partial enclosure, such as a fume cupboard, was also considered and rejected, as this would involve both restricted access implications and potential exposure to fumes when the fume cupboard was opened for access. After a thorough
IFHE DIGEST 2019
Part of the plant room in a production facility.
The design of the booth was more of an iterative process, with several designs considered in order to achieve the initial design intention of separating the operator from the process as much as possible
examination of several options, it was clear that adopting a side-flow booth strategy would answer both the operational and safety elements of the brief.
The side-flow booth The side-flow booth acts like a walk-in wind tunnel, promoting horizontal laminar airflow by inducing air from the face of the booth to the rear. Each of the three booths was designed as a corridor, with the purification equipment on one side and the oven and preparation table on the other. These process areas on opposite sides of the booth form the fume control zones with an operator breathing zone in the centre, providing space for operator movement and unrestricted access to
equipment without risk of exposure to fumes. Consideration of the interface between
the operator and the process was vital to ensure unforeseen fume exposure did not take place. ‘Body wake’ was an important factor in this regard as turbulence from the operator’s movement could affect the laminar airflow of the fume control zones in the process areas. Consequently, it was important to fully understand the process and model operator movements in the booth to ensure the breathing zone consistently provides uncontaminated air. Every design detail was considered
to minimise disturbance of the laminar airflow. To minimise the extracted flow rate, the air is directed to where it is required and every element of the layout has been designed to accommodate this airflow management strategy. For example, a half height door has been fitted to each booth entrance and a corner cut off has been used to remove the unused cross sectional area, optimising the airflow. The arrangement and orientation of
flasks, oven and corridor have been designed to ensure that the operator stands side or shoulder to the airstream, reducing the wake effect of the body by orienting the narrowest point of the operator’s form towards the airflow. Any Fully co-ordinated plant room pipework. wake effect that is produced takes place
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