Fume extraction fans are required to exhaust hazardous substances and odours out of mortuary and autopsy rooms via downdraught ducting systems. Corrosion resistant fans manufactured from chemically resistant polypropylene are the preferred material, withstanding the harsh processing chemicals used in post mortem, autopsy and inquest procedures. The use of exhaust fans enables the system to vacuum any toxic particles through ductwork and exhaust them safely.
A post mortem room requires a fresh air supply introduced at high level, above the observation area to protect personnel or visitors and to prevent interruptions to the air flow pattern provided by downdraught benches. According to NHS Wales the minimum recommended total fresh air supply rate to a post mortem room is 10 air changes per hour. In high risk cases a minimum of 12 air changes per hour is advised along with maintaining a negative pressure, HEPA filtration and downdraught ventilation system. However, the number of air changes is dependent on the individual specification of the room and factors such as room size, the chemicals produced and the type of equipment used should all be considered. As stated by the Department of Health the ventilation system of a mortuary should be designed to minimise the spread of odours and airborne pathogens by being isolated from other ventilation systems such as air handling units, where possible.
Downdraught Ventilation Equipment in Morgues and Autopsy Rooms
Downdraught benches ventilate the air across the top of the bench and out through a rear extract. This type of equipment is favoured due to the air flow drawing the contaminants down beneath the operator as they work. This prevents the contaminants reaching the operator during or after any processes and ensures the air flow is not interrupted. It is important that the air can constantly flow and that systems are meeting all the criteria. A system with an interrupted air flow would be less efficient and pose risk to the operator.
Downdraught benches with adequate ventilation are necessary equipment in morgues and autopsy rooms for handling formalin-fixed preserved organs and tissues. There are hazardous xylene, formaldehyde and hot paraffin fumes present in autopsy laboratories. It is crucial to have the correct mechanical fans that will achieve the duty required to extract fumes effectively.
While Axair cannot supply or specify the set up of downdraught ventilation systems, we can work with contractors, installers and system designers to ensure the industrial fan is suitable to achieve the required airflow, pressure and system performance required for the room specifications. This includes ensuring an accurate fan size is chosen to avoid higher level gases and toxins being present around personnel.
An example of an inaccurate fan selection of ventilation system was discussed by Centres For Disease Control and Prevention in which a downdraught table that had been modified to have a 800 cubic foot/minute exhaust flow rate exhausted up to 50% of the rooms air supply. The slot exhaust at the head of the work bench exhausted the remainder. To detect gas removal the tracer gas sulfur-hexafluoride was released at key points along the table. At table height and up to 10cm above the table no gas was detected and downward velocities of 725 and 1,000 feet/minute (ft/min) were recorded. When released at nose level height, gas was detected and downward velocity was 60 to 90ft/min. From this it was concluded that by modifying the downdraught bench it would further reduce the exposure to formaldehyde to 0.3ppm. The modification options would be to increase fan size or place an additional ventilation system directly above the table.
Alternative Ventilation Control Methods
When specifying the correct ventilation equipment for your application it is important to consider the type of contaminants generated and the area of capture required to ensure a safe working environment.
Back and side draught tables draw contaminated air through the back or sides of the system and have the option of added HEPA filtration systems. An added benefit of this type of system is that it can be converted into a full enclosure, this provides further protection from exposure to harmful substances.
Another option is to use a fume extraction arm which can can be placed in various desired working areas due to its flexibility. The fume extraction fan is integrated into the system via ducting that is attached to the arm, this allows the hood at the top of the arm to vacuum the toxic fumes from the working area. However the surface area of the extraction arm hood is much smaller than the area of a downdraught bench which means there is a risk of not capturing the contaminants quick enough allowing them to escape and reach the operator.
In conclusion the downdraught bench is the preferred choice of equipment for mortuary and autopsy rooms due to its large surface area that enables a large capture zone. Fume and Dust particles are generally heavier than air and gradually sink with the pull of gravity so equipment that draws contaminants in a downward air flow is more effective. A downward airflow that is uninterrupted prevents the contaminants from floating up towards the operator and provides the most protection.
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Corrosion Resistant Polypropylene Fans
Corrosion resistant polypropylene fans are best suited to handle the use of formaldehyde within this type of environment as they can withstand harsh chemicals without rusting or corroding. Maintenance of the downward draught fume extraction systems is crucial for mortuary and autopsy rooms due to the risk of staff and visitors contracting infectious diseases from airborne droplets, the cacogenic nature of preservatives chemicals and to eliminate any build up of foul odours. There are certain regulations that must be met according to the latest guidelines set by COSHH. When considering the build of a fume extraction system it is important to ensure there is no risk of reintroduction of the exhausted air being blown back into the building through vents or windows so the positioning of the fans and ducting is crucial.
The Axair ‘S’ range fans are designed to provide high air flow rate against medium system pressures.
The Axair STORM ‘ST’ range fans are designed to provide a relatively low air flow rate against elevated system pressures.
The ATEX ranges are available for Category 3G Zone 2 applications and can be supplied with EEx nA or EEx d motors to order.