The HSE is the UK watchdog for work-related health, safety and illness matters, within which it develops strategy and policy, provides advice and guidance and undertakes inspection and enforcement where appropriate. Their guidance in respect of Portable Dust Control and Extraction Equipment derives from both general legislation and industry consultations and is presented within Construction Information Sheet no. 69 - Controlling construction dust with on-tool extraction. The full document can be accessed online at http://www.hse.gov.uk/pubns/cis69.pdf . We have endeavoured to accurately reflect their guidance in this overview. Phraseology and terminology used is consistent with the HSE output but it should be stressed this is our understanding of the subject, including interpretation of publicly available information.
The main legislation covering construction dusts is the Control of Substances Hazardous to Health Regulations 2002 (as amended) – more commonly known as COSHH. The main requirement of COSHH is to prevent workers being exposed to such substances. Where this is not reasonably practicable, this exposure needs to be adequately controlled. In a discussion document, the HSE listed "the main dusts of concern" as:
Silica is a common substance present in large amounts in natural materials such as sand, stones and rocks including sandstone and granite. It is also commonly found in many construction materials such as concrete, mortar, bricks and blocks. The silica is broken into very fine dust (also known as Respirable Crystalline Silica or RCS) during many common tasks such as cutting, drilling and grinding. It is often called silica dust. ‘Mixed dusts’ (see below) will also be created during these tasks. However, the silica will be the main risk.
Wood is widely used in construction and is found in two main forms; softwood and hardwood. Other wood-based products are also commonly used including MDF and chipboard.
There are a number of construction products that can produce mixed dusts of varying degrees of harm. The most common ones include gypsum, cement, limestone, marble and dolomite. These may contain small amounts of silica but these amounts are not significant enough to be the main risk.
Portable Dust Extraction Equipment (also referred to as Industrial Hoovers, Industrial Dust Extractors, Industrial Vaccums, or Construction Vacuums) is classified as H, M or L Class:
Carcinogenic substances such as asbestos. An H Class filter is required to have a Filter Leakage no greater than 0.005% of the collected dust.
Concrete and mortars (Silica) Man-made woods (MDF) and Natural woods (Oak, Beech). An M Class filter is required to have a Filter Leakage no greater than 0.1% of the collected dust.
General construction dust/waste and lower-toxicity materials. An L Class filter is required to have a Filter Leakage no greater than 1% of the collected dust.
HSE advise M Class dust extraction should be the default choice for Construction Sites where concrete, mortars and man-made wood products are being worked.
An M Class dust extractor should include the following features/functions:
Compliance with these requirements will be achieved using a variety of designs and equipment configurations. Compliant equipment should display an external label on the equipment and a smaller item on each filter.
H Class filtration is specified for handling hazardous dust and waste. BUT just fitting an H Class filter to a Dust Extractor will not make it suitable for collecting hazardous substances. A H-rated Dust Extractor will have a number of features over and above the H-spec filter. Some of these features (such as screw-fitting blanking plugs) are designed to contain residual waste within the equipment whilst it is being transported Rigorous handling procedures are required for hazardous waste as are routines for de-contaminating equipment following use.
An H specification filter will block very fine dust particles but as a consequence, will clog more easily if presented with a large volume of waste. The consequent reduction in airflow will result in poorer dust control and reduced extraction rate. For this reason, if using an H Class product for high intensity work, some form of continuous/automatic filter cleaning is advisable to maintain performance. Alternatively, some form of Dust Pre-Separator or Interceptor could be used to collect dust in advance of the filtration stage. Properly configured, pre-separation can result in less than 10% of collected dust being presented to the filter, the twin benefits being extended periods of full suction between filter cleaning events and improved filter life.
L Class equipment is suitable for handling Mixed Dust products as described at the begining of this article. It will commonly be used for general site work and in many cases will support on-tool dust extraction, where the materials involved do not fall into either the M or H classification. Moreover, it should be safe for handling small volumes of low silica content products.
Terms commonly used include On-tool Extraction and Dust Control at Source. It is generally the case that most machinery, large or small, can be designed and equipped with containment features, complemented by connection ports for extraction systems:
Where on-tool/on-machine facilities are not present, positioning an open-mouth collector device in line with the expelled dust may provide an adequate degree of dust control, although it is most lilkley a more powerful extractor will be needed (when compared to a comparable on-tool set-up)
Factors to consider in selecting a dust extractor for a specific application or trade will include:
New H and M Class Dust Extractors should be equipped with a bagging facility. This may be internal or external to the unit. The intention is to ensure waste can be contained and disposed off with minimal spillage.
L Class compliant extractors do not have to include a bagging facility, although the feature does appear on some product.
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What is the difference between L, M and H class vacuums?
The classification relates primarily to the specification of the filter. L class filtration is suitable for Low hazard materials, M class for Medium hazard, H for High hazard. L class filters are required to have a leakage no greater than 1% of the collected dust, M class no greater than 0.1% and H class no greater than 0.005%. Put simply, a H class filter will block particles that would pass through an L or M class filter.
What class of vacuum do I need on a building site?
For construction works, general waste is considered Low hazard. Concrete and mortars are rated medium hazard as are some natural woods, notably beech and oak; engineered woods such as MDF are also Medium rated. Carcinogenic substances such as Asbestos are classed as High hazard.
Can I upgrade my L class vacuum by changing the filter type?
You may well be able to fit a higher specification filter to your basic vacuum but that will not change its classification and it could reduce its performance. In practical terms, M and H class filters have a finer weave (than L class) so as to block finer dust particles. But inevitably, this also constricts airflow. So M and H class vacuums have other features which compensate for this condition e.g. larger motors, pre-separation elements, integral filter cleaning. Put simply, there is much more to vacuum or dust extractor performance than the filter.
What are the three key considerations in selecting a dust extractor for construction work?
Product selection should mirror the end-to-end requirements of the work. Firstly, select a filter type that is suitable for the materials you are going to be dealing with. Secondly, consider the performance requirements of the work you are doing e.g. volume of dust and waste being collected, intensity of work, accessibility (determines hose length required). Thirdly, consider how the waste will be contained and disposed of. Effective dust control starts with capture of dust at the point of creation, ends with dust-free disposal of the waste and in between, ensures exhausted air from the vacuum system is devoid of harmful particles.