This circular provides specific guidance on the control and enforcement of Respirable Crystalline Silica (RCS) issues associated with kerb, paving and block cutting in the construction industry. Further details can be found in SIM 02/2009/01, from which the information below is taken.
Kerb, paving and block products are used extensively throughout the construction industry. These products are often cut to the required size using hand-held cut-off saws without proper dust control measures. This results in the operator and other nearby individuals being engulfed in large clouds of RCS containing dust.
Serious health effects, such as silicosis or lung cancer, can result from this exposure. This is due to the ability of the fine RCS particles to penetrate deep into the lungs (more details on RCS and its associated ill-health effects can be found in SIM 03/2008/09: Silica dust Guidance and enforcement). It is not precisely known how many cases there are of RCS related disease linked to the construction industry although recent HSE funded research1 has indicated the number is likely to be more than is shown in reported statistics. Through statistical estimation based on exposures experienced up to 50 years ago; this research suggested that over 500 construction deaths from silica related lung cancer occurred in GB in 2004. This equates to around 10 construction workers a week and suggests silica is currently the second most important cause of occupational lung cancer after asbestos. Forthcoming work will look at predicting future estimates due to more recent exposure levels.
Despite these statistics the industry has a poor appreciation of the problem2. While 'dust' in general is seen as a problem by many, there is little understanding of the real issues associated with it3.
Where it is not reasonably practicable to prevent exposure to RCS by avoiding its generation, control at source should be achieved in the following ways:
Consideration should first be given to 'dust free' methods such as the use of block and slab splitters. These work by positioning the material (e.g. pavers or slabs) between an upper and lower 'blade' through which a force is exerted until the material breaks. There are three basic types:
These devices are capable of cutting many paving and block materials. However, they require a degree of skill to use accurately and effectively. There is also a manual handling issue associated with lifting and placing heavier items in-between the cutting 'blades'. If the finish required is for a perfectly straight edge then block splitters may be unable to achieve this especially if the cut only requires small amounts of material to be removed close to the edge of the block.
Where 'dust free' methods are not appropriate, it is likely that a hand-held cut-off saw (also known by names such as Stihl saw, skill saw, disc cutter, whizzer or con saw) with appropriate water suppression is going to be the most reasonably practicable solution. This has the additional benefit of extending the lifespan of diamond tipped blades where these are used.
The water is applied onto the rotating cutting disk via two spray heads or jets normally attached to opposite sides of the guard. A minimum flow rate of around 0.5 litres per minute is required for effective dust suppression4. Low flow rates will not achieve sufficient dust suppression. Very much higher flow rates do not improve dust suppression but do increase the need to refill any container more often.
The water supply is controlled by an on-off valve fitted to the saw which often has an in-line filter installed to prevent the heads becoming blocked. Water can be connected to this valve from a number of sources. Where possible, especially for larger jobs, a direct connection to a mains supply via a hose is preferable. This provides an unlimited water supply at a continuous flow rate. However, mains supplies are not always readily available or appropriately situated. An alternative solution is to provide one of the proprietary large water tanks with running pump that are now available.
For small jobs or infrequent cutting operations the simplest way of supplying water is via a portable polypropylene hand pump bottle. This contains around eight litres of water that is pressurised by hand. However an effective flow is sustained only for a limited period (up to 4 minutes4) before re-pressurisation is required - see video Time to clear the air! Using cut-off saws for cutting kerbs and flag paving
There are a number of potential problems that may arise in association with the use of water suppression.
Where the use of water suppression is difficult or inappropriate, ventilation extraction can provide an effective alternative. It has the additional benefits of being safe to use with electrical equipment and not generating slurry.
However, the rate of extraction needs to be sufficient to capture the RCS particles generated by the cutting process. This extraction rate is dependent upon a number of variables such as blade speed, gap size/extent of blade coverage etc. On-tool extraction is also best suited to work involving straight lines or flat surfaces. Extraction is reduced where work is undertaken on curves, bends and uneven surfaces or at the edge of the material. The same is true where the blade is not properly enclosed by a hood, guard or brushes. The more effective devices usually have the extraction hoods built into the tool as an integral part of their design.
Exhaust from these systems must be filtered. Vacuums used for dry cutting should be fitted with an H class 13 HEPA filter to EN60335-1. Emptying these will require the wearing of suitable RPE.
Dutyholders should only use on-tool exhaust ventilation after a careful and critical selection process. This includes obtaining the relevant information from equipment manufacturers/suppliers.
Note that equipment can be made cumbersome by such systems which can also be easily damaged. Effective maintenance procedures are thus important.
Effective engineering controls should be sufficient to significantly reduce the RCS risks associated with kerb, paving and block cutting in most instances. To deal with the residual risks the following are applicable:
Even with extraction or water suppression, individuals will still need to wear RPE to minimise the remaining risk. This is because the actual level of RCS exposure for each piece of cutting work will be unknown. "Adequate control" cannot also be guaranteed by water suppression/LEV systems as these are not fully reliable due to the many factors which could reduce their effectiveness. RPE is therefore required to protect against this unknown and variable residual risk.
RPE should have an assigned protection factor of at least 20 (e.g. FFP3 filtering facepiece disposable masks or orinasal respirators with a P3 filter). Wearers should be appropriately trained and face fit tested for the equipment. A qualitative fit test is acceptable (see OC282/28: Fit Testing of Respiratory Protective Equipment Facepieces for further information on face fit testing)
Disposable masks should be replaced every shift or when damaged. Orinasal filters should be renewed frequently; probably at least weekly. A supply of suitable spares should thus always be available. A "loose-fitting" type of respirator (e.g. powered hood, helmet or visor) should be worn by workers who have beards or are unable to obtain an adequate fit from the disposable or orinasal masks.
Access to cut-off saws needs to be restricted to those individuals who are appropriately trained. Blade selection is an important consideration. There are two main types; abrasive and diamond tipped. Although initially more expensive the diamond tipped blades offer a longer working life, a constant depth of cut and generate less RCS. A normal abrasive blade wears as it cuts and so the depth of cut will reduce over time. This produces a secondary issue when used in association with LEV as the captor device may not automatically compensate for this wear.
Cut-off saws need to be used in the most efficient manner. For example, sawing a flag to half its depth will usually be adequate to ensure it breaks in the required place after a few taps from a hammer. The result is a significant reduction in the amount of RCS generated when compared with sawing the full depth of a flag.
Some form of segregation may be required depending upon the risks associated with residual RCS levels or the ejection of shards/fragments during the cutting process. This might involve screening or other such physical barriers attached to scaffolding or inside buildings. Alternatively the cutting could be undertaken in designated areas, a particular sequence or by limiting the number of persons in the vicinity.
Note that due care has to be taken when segregating the work that this does not interfere with emergency or other such arrangements.
Adequate ventilation will also be required where cutting is undertaken in a tented/sheeted/confined area. This is because any uncontrolled dust will not easily disperse and fumes will be generated with the use of any petrol engine saw. Where natural ventilation is insufficient mechanical ventilation should be provided.
All cutting operations should be undertaken with appropriate eye and hearing protection. These should not interfere with the effectiveness of the RPE provided. Suitable clothing should also be worn. Modern fabrics are less likely to retain dust than cotton and suitable overalls should be selected on their dust retention and release characteristics. Operators may also need to wear waterproof trousers or leggings to prevent them becoming wet where water suppression is being used. Concern about wet trousers is one of the reasons cited for water suppression not being used.
While the control measures above are important for reducing RCS risks on site, they need to be underpinned by the effective implementation of appropriate management arrangements as required by COSHH. Where appropriate a dutyholder should be able to demonstrate:
HSE is working to develop a framework within which decisions about the appropriateness of Health Surveillance for silica exposed workers can be made. In the interim this means that decisions on health surveillance (and chest x-rays in particular) will need to be made on a 'case by case' basis by competent advisers taking into account the relevant factors.
The primary legislation concerning RCS risks is the Control of Substances Hazardous to Health Regulations 2002 (as amended). The current WEL was adopted on October 2006 and is 0.1mg.m3 over an 8 hour TWA reference point.
It is important to note that while RCS is not classified under the existing arrangements as a carcinogen under COSHH, it can be considered a suspected carcinogen. For such substances employers need an active precautionary policy of prevention and control based on the up-to-date knowledge of the substances. In line with this precautionary approach a more rigorous control regime is expected. This includes a high standard of RPE where powered tools are in use.
Exposure to RCS is considered to constitute a 'serious health effect' within the EMM framework. The likelihood of this occurring is set out in the risk matrix below:
| Application/Interpretation | Likelihood | ||||
|---|---|---|---|---|---|
| Probable | Possible | Remote | Nil/Negligible | ||
| Serious health effect | Silicosis Lung Cancer |
Highly likely that exposure that could result in most people being affected would occur. (No controls or ineffective controls) |
Exposure to multiples of the control limit.(One effective control) | Control limit for RCS(Minor deficiencies in controls) |
Benchmark represented by effective use of control measures (Correct use of expected controls) |
The serious health effects do not arise from the acute effects of exposure to RCS. The conditions have long latency periods and result from repeated occupational exposures. The risk of developing disease for construction workers depends on the accumulated dust burden (i.e. dose) of individuals over many years. Therefore every occupational exposure episode is significant. Each exposure episode builds on previous exposures and this dose will add to the platform for future exposures and so the risk of developing ill health increases. Consequently there is a need to control every single occupational exposure.
A number of factors (such as the silica content of the material, the duration of the task and the type of blade involved) affect the level of exposure for each cutting activity. However, as these factors are often unknown or variable, the likelihood of developing a serious health effect depends primarily on the presence and effectiveness of controls. The likelihood of developing ill health is considered to be either probable or possible where there are inadequate control measures.
The following matrix provides guidance on the likelihood of ill heath occurring according to the level of control, and the associated initial enforcement expectation. Note that the provision of suitable and effective RPE would be sufficient to comply with a PN as an interim measure. However, in such instances an IN should be issued for the provision of engineering or other controls.
| Initial enforcement expectation | |||
|---|---|---|---|
| Control failure | Serious health effect likelihood | Consider PN | Consider IN |
| No control measures (i.e. no water suppression, LEV or RPE) |
Probable |  |
|
| Ineffective control measures (e.g. water suppression weak/no flow and RPE badly worn/ damaged/ incorrect APF/ no face fit) |
Probable | |
|
| No or ineffective water suppression or LEV but effective and suitable RPE | Possible | |
|
| Effective water suppression/LEV but no suitable and effective RPE | Possible | |
|
Further details on the enforcement of management issues and (sub) contractors etc can be found in SIM 02/2009/01
Further general guidance on risk and enforcement in relation to RCS is contained within:
Further advice and support on this issue can be obtained from by contacting your local HSE office construction department.
There is a significant amount of information available relating to the control of kerb, paving and block cutting together with RCS risks in general. The most relevant are:
Recent additions and changes
Making a difference - Judith Hackitt