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Why Downdraught? The benefits of downdraught extraction.

When an engineer considers the appropriate method of extraction for a specific dust or fume issue, they must examine a wide range of factors. Considerations including the contaminant itself, the process generating the contaminant, operator behaviour, and the general working environment.

Particulate or Fume?

Factors relating to the contamination include whether it is a particulate or a fume – a typical fume or gas will require significantly less effort and energy to capture. If we are looking to capture a dust, the contaminant would also be examined to understand how fine it is – a lighter dust will always have less momentum which would make capture easier, but may also be more easily inhaled so can therefore be more hazardous. If considering a fume, we would wish to understand whether the fume can be captured by filtration or must be exhausted to atmosphere.

The process in question will influence how much energy is imparted to the contaminant – heavy grinding will give particles significant momentum and make capture more difficult, while a lighter process involving sanding or dispensing may produce a dust or fume which is easier to capture but may be initially released over a wider area.

Operator Behaviour

Operator behaviour is an often overlooked aspect of specifying a dust extraction solution. When visiting a customer, our view is always that a user can choose whether the solution supplied will succeed or fail. A failure to engage the operator in the selection process will lead, at least, to a lack of belief in the extraction solution; and sometimes even worse results.

Working Environment

The general working environment must also be considered; higher levels of air movement in an environment will naturally reduce contaminants but for more hazardous substances can lead to contaminants being dispersed over a wider area before capture. Equally, generation of dust in a calm and sheltered environment may mean the dust is easier to capture but the effects of excess air movement introduced by the dust extraction system may cause process issues.

As experts on the use of downdraught benches and downdraft tables as solutions to dust and fume issues, we consider on a daily basis how to ensure our products can best address these issues.

So why is a downdraught bench potentially a highly effective solution to many dust or fume issues?

Firstly, a large capture area can remove many of the concerns around the contaminant itself. An extraction arm is often considered as an alternative to a downdraught bench. These systems typically have capture zones the size of a football. If we cannot reduce the velocity of a contaminant sufficiently before it escapes this capture zone, it will escape and be easily inhaled by an operator. We can quickly see that the potentially huge capture zone of a downdraught table allows much more time for a contaminant to slow and be captured; a large downdraught bench can provide a capture zone the size of a coffee table or larger and very few inhalable dusts can continue at high velocity through a zone this size.

Downdraught tables provide flexibility in filtration options, again allowing a wide range of solutions to be implemented relatively easily. As filtration mechanisms are not necessarily fixed in this type of system, filters can be specified to suit the process with appropriate filter grades or types used.

Operator behaviour is a limitation to many types of alternative extraction system and is a huge advantage for downdraught benches. While an operator must move an arm regularly to maintain the extraction zone in the correct position, in most cases all an operator must do when using a downdraught table is work on the bench surface, and this will ensure capture. Only high volume low velocity systems such as benches and booths offer this flexibility to the operator.

However, as above we must still consider operator engagement. Many larger installed extraction systems are supplied based on desktop quotes and drawings, without operator involvement in specification. Downdraught benches, being stand-alone and self-contained, allow the system to be demonstrated to the user prior to purchase. Operators are able to feed back on suitability and determine how their own methods will work with the downdraught system.

Key advantage of a Downdraught Extraction System

Finally, and perhaps one of the greatest advantages to a properly specified downdraft bench system; most dusts and fumes tend to move downwards. Overhead hoods work to draw contaminants upwards, past the operators breathing zone; downdraught benches draw dust and fumes down away from the operatorAirbench Diagram. This takes advantage of gravity while avoiding exposing the user to potentially worse dust concentrations. This is particularly relevant to solvents and similar fumes which almost always tend to disperse downwards; but even light dusts tend to settle downwards.

In conclusion, a properly specified downdraught bench system not only solves a wide range of dust issues, but takes advantage of natural phenomena to make an engineer’s job easier. AirBench Ltd offer on-site demonstrations across the UK and work with distributors in both the EU and Worldwide to supply our dust and fume extraction systems.

Contact us to discuss the application of downdraught technology to your own dust or fume issue.

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Why choose AirBench?

AirBench Ltd are the UK’s leading manufacturer of downdraught benches and cross draught extraction systems. We have more than 10,000 extraction systems in service in the UK and overseas. Along with our range of coolant mist filters and air cleaning systems, we are actively helping businesses across many industries solve their workplace dust and fume issues.


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