1. Kerb, Paving and Block Cutting
Silica Risks from
Kerb, Paving and Block Cutting
Who are you:
HSE’s priority inspection topic for the forthcoming year – Silica
However there are other health issues such as manual handling

2. What is the Problem? One of the most abundant materials on earth
Found in varying amounts in many materials:
Sandstone (>70%)
Sand, gravel, flint (up to 70%)
Cement, mortar, concrete (25 to 70%)
Brick (up to 30%)
Crystalline silica is one of the most abundant minerals on the earth.
There are different crystalline forms of silica, with the most common one being quartz. Quartz is found in varying amounts in almost all types of rock, sand, clay, shale and gravel. For example, sandstone is more than 70% quartz, whereas granite might contain 15-30% quartz.

3. What is the Problem?
Silica is found in sand but is not a hazard as it is not fine enough to be inhaled – see next slide

4. Why is it a Problem? Particles need to be “respirable” to cause harm
Issue is Respirable Crystalline Silica or RCS
RCS particles can penetrate to deep lung
Usually invisible under normal conditions
The act of cutting, drilling, grinding or polishing silica containing products such as kerbing, paving, blocks and concrete produces airborne dust containing a range of crystalline silica particle sizes, some of which can be inhaled. Larger particles are prevented from being inhaled by filtering by the nose and coughing.
Inhalable crystalline silica approximates to the fraction of airborne material that enters the nose and mouth during breathing and is therefore available for deposition into the respiratory system. Respirable crystalline silica is the element of that inhaled material that penetrates to the gas exchange region of the lung. RCS is also known as respirable -quartz, cristobalite or ‘free silica’. Very fine silica can be inhaled deep into the lungs where it causes damage.

5. Why is it a Problem?
RCS is not visible under normal lighting conditions. This slide shows the difference between normal lighting conditions on the left where the RCS cannot be seen and a dust lamp on the right where RCS is highlighted. This is a ‘low energy’ process and so the amount of RCS produced with power tools is significantly moor.

6. Why is it a Problem? Main concern is SILICOSIS Lung Disease
Reduced lung function
Can cause death
Disease continues to develop when exposure has stopped
Can also cause lung cancer and COPD
A number of health effects can result from the ability of the fine RCS particles to penetrate deep into the lungs:
Silicosis – A slow, progressive, irreversible disease that usually develops many years after initial exposure. Symptoms can include chronic cough, phlegm and mild to serious breathing difficulties. In severe cases death can ensue. Silicosis is diagnosed by chest X-ray where the presence of scar tissue on the lungs is visible. The highest risk of developing silicosis is from exposure to the freshly fractured fine particles of RCS that are generated during many common workplace tasks such as drilling, cutting, grinding or polishing.
Acute Silicosis – Individuals who experience exceptionally high exposures over a few months or years can develop this rapidly progressive and often fatal condition (after exposures in the order of 1.5 mg m-3 on a daily basis for a year or two – doesn’t tally with 1.0mg probable risk level using in emm) ref. This can result in death within a few years of exposure.
Lung Cancer – Heavy and prolonged exposure to RCS under the conditions that produce silicosis can cause lung cancer.
Chronic Obstructive Pulmonary Disease (COPD) – There is evidence the individuals who work with RCS have abnormal lung function suggestion of COPD although it isn’t clear if this is due to silicosis rather than separate from it. COPD is an umbrella term that covers emphysema and chronic bronchitis. It is characterised by airflow limitation and is not fully reversible. The symptoms are the same as for silicosis – cough with phlegm, wheezing and breathing difficulties. It too can result in death.
What could this mean in practice for a construction worker exposed to RCS above the exposure limit over a long period, for example from the age of 20 to 40, who goes on to develop associated lung disease? In the early stage of lung disease an individual may notice some occasional breathing difficulties, occasional breathlessness when running and possibly bouts of persistent coughing. Later on as the disease progresses an individual may need an inhaler and find that they cannot sleep properly through the night. They cannot play sport and walking long distances may also be difficult. By the time the individual reaches 60 they could be housebound and in need of regular portable oxygen from a cylinder via a mask. Their doctor may be advising them that they could soon need a wheel chair. In layman’s terms this means “a young healthy lad starting work at 20 who cannot breathe at 60”.

7. Why is it a Problem? Statistics are imprecise:
Affects 10 – 20 % of construction workers???
Over 500 silica related deaths in 2004 –
Over 10 a week
Research suggests silica is the second most important cause of occupational lung cancer after asbestos
It is not known for sure how many construction workers are exposed. One HSE study put the number of workers regularly exposed to RSC at around 10% of the total workforce. Another HSE funded study has taken data from the international CAREX database and estimated that between 1990 – 93 around 450,000 workers were exposed. Whatever the true figure it is likely to be significant.
It is also not known for sure how many cases of silicosis and other silica related diseases there are, but the number of cases is likely to be more than is recognised in the available reported statistics. For example the recent review undertaken by HSL as part of the Silica Baseline Survey indicated that under the Surveillance of Work-Related and occupational Respiratory Disease (SWORD) 52 cases of respiratory disease attributable to silica in the construction industry were reported between 1996 – This represented 14% of all such industry reports for that period.
However, on the basis of risk estimates many more cases would be expected. Recent HSE funded research which indicated that there may have been around 800 deaths from silica related lung cancer in GB in This is a statistical estimate obtained by using scientific evidence of the risk of lung cancer in silica exposed populations, and combining that with information on the number of cases of lung cancer in the overall population and estimates of the proportion of people exposed to RCS, using established methods for calculating the proportion/number of cases that would not have occurred in the absence of the exposure.
Of these 800 deaths over 500 are linked to the construction industry. This equates to 10 people every week. The research suggests that silica is the second most important cause of occupational lung cancer after asbestos.

8. Why is it a Problem? Industry appreciation of the risk is poor:
People not aware of these health risks
Think that it is ‘just dust’
Underestimation of exposure levels
Require convincing that control measures work
Industry appreciation of the risks from RCS is probably variable at best. The Silica Baseline Survey concluded that while many activities are capable of generating RCS concentrations considerably above the exposure limit, most of the employers visited during the study had underestimated the extent of exposures and in many cases had not made the implementation of exposure control a priority.
Industry research for Speedyhire goes further. This indicated that dust is seen as a problem by almost everyone and as a serious problem by 27% of managers and 21% of operatives interviewed. However, there was not much understanding of the different types of dust and their effects on health. No operatives mentioned asthma or silicosis unprompted when asked what health concerns they had about dust. While there was a general understanding that dust was bad for their health, and that certain types such as asbestos were worse than others, people were unclear in quite what way it was bad.
When it comes to the control of dust the research found that the most common action taken in response to dust was the wearing of RPE, although this was criticised by the workforce as often being uncomfortable and impractical to wear. In addition tools that minimise dust or extract it were seen by many workers as ineffective; there being a general feeling that you can never eliminate dust on a site although you may be able to reduce it.
Given the above it is apparent that a significant change in the industry’s approach to this issue is needed.

9. How Much is a Problem? COSHH sets WEL for RCS at 0.1mg/m3 (8hr TWA)
You are at risk if the dust you breathe in over a full shift contains more RCS than the amount shown next to the penny. This puts it in context that the amount that we are talking about is very small. Remember that:
this is the ‘maximum’ legal limit. Dutyholders should be aiming to get their exposure levels below this.
It is o.1mg/m over an 8 hour reference period. A higher exposure over a shorter period may thus not exceed the Workplace Exposure Limit (WEL) when averaged out – see next slide.

10. How Much is a Problem?
15 years daily exposure to RCS dust at average airborne concentrations (for an 8-hour shift) of:
Risk of developing silicosis within 15 years following cessation of prolonged daily exposure
0.02 mg.m-3
0.25%
0.04 mg.m-3
0.5%
0.1 mg.m-3
2.5%
0.3 mg.m-3
20%
It has been possible to estimate the risk of developing silicosis from exposure levels. A recent HSE review (HSC Consultative Document Control of Substances Hazardous to Health Regulations 2002 (as amended 2005). Proposals for a Workplace Exposure Limit for Respirable Crystalline Silica) provided quantitative risk estimates based upon a study of hundreds of workers from a particular Scottish coalmine and are thought to be a reasonable representation of risk from other exposure settings. It shows that prolonged daily exposure to levels just 3 times the WEL can result in a significantly increased risk of developing silicosis.
This risk depends on the accumulated RCS burden (i.e. dose) of individuals. Each exposure episode builds on previous exposures (often inadvertent, unknown and unrecorded) and this dose will form the platform for future exposures and so the risk of developing disease increases. Consequently each exposure is relevant and increases the risk of developing ill health later in life. Therefore it is extremely important that exposure episodes are not considered in isolation.

11. How Much is a Problem?
When work like this is seen what does it actually mean in relation to the previous slide. i.e. is it above or below the WEL?

12. How Much is a Problem?
The amount of RCS generated is dependent upon many factors – silica content, type of blade used for cutting, blade speed. This shows results from one set of measurements relating to exposure associated with slab cutting – remember the daily limit is 0.1mg/m.
When calculated in terms of the 8 hour time weighted average the daily exposure for 15 minutes operating the diamond blade is o.o5mg/m3 And for the resin blade 0.15mg/m3
Although the former is below the WEL for this duration, remember the duty is to reduce exposure so far as is reasonably practicable. It is therefore still unacceptable. Exposure levels over 1.0mg/m3 represents gross contamination.
15 min SLAB CUTTING (40% silica) in open air, no control
Diamond blade = RCS exposure of 1.6 mg/m3
Resin blade = RCS exposure of 4.8 mg/m3

13. Control Solutions Can the risk be eliminated?
Can a ‘dust free’ method of work be used?
The first requirement of COSHH is to prevent exposure where reasonably practicable. The possibility of substituting the material with one containing less/ no RCS or redesigning the process altogether should therefore be investigated. Appropriate material sizes can also be selected so as to minimise the amount of cutting required. These principles also link in with the duties of designers under CDM However, given the prevalence of silica in the materials and products used in the construction process, such preventative methods may only sometimes be reasonably practicable.
Where it is not reasonably practicable to prevent exposure to RCS can ‘dust free’ methods of work be used. There are some tasks that can be undertaken using tools that are essentially ‘dust free’ or replace more dust generating activities. Block and slab splitters are especially versatile and capable of dealing with materials from brick size up to flagstones. There are three basic types which all use the same principle of compressing the material between an upper and lower blade until the paving snaps:
A manually operated machine with a continuous flat blade. This is suitable for smooth or regular paving materials. In addition to this radial adaptors are available to enable specific curves to be cut.
A manually operated machine with a number of spring mounted teeth. This is suitable for cutting paving with an irregular surface as the use of a continuous flat blade places uneven compression forces across the materials surface leading to a fracture in the wrong place.
A hydraulically operated machine, the larger versions of which are capable of splitting those blocks too thick to be cut using force. The hydraulic pressure can either be generated manually or by electrically pumped system. However, the former can be slow to use and will often not be reasonably practicable for large scale work

14. Control Solutions Water Suppression
Process changes and dust free methods of work are limited in number and restricted to certain tasks. This still leaves a number of operations requiring the use of power tools with the potential to generate large amounts of RCS. The most common means of controlling the RCS dust produced in these circumstances is through water suppression. The method of water suppression for power saws is the same in all instances – a supply of water to the blade (water may be used on abrasive wheels and diamond tip blades). This supply is facilitated by an attachment that allows an external source of water to be secured.
Water flow rate
Studies have shown that a minimum flow rate of about 0.5 litres per minute is required to optimise dust suppression. Low flow rates will reduce dust suppression performance. Very much higher flow rates do not improve dust suppression but do increase the need to refill any container more often.

15. Control Solutions Water Sources
External water sources can be provided in a number of ways. Where possible a direct connection to a water main via a hose is the best option as water can be supplied at a continuous flow rate without the need for someone to pressurise the water tank (see below). However, mains supplies are not always readily available or located close enough to the work area. A common solution is the use of a portable supply.
The simplest type of portable supply comes in the form of a hand pump bottle which is supplied by most major cut-off saw manufacturers and plant hire companies. Typically it consists of a polypropylene bottle containing approximately eight litres of water. The bottle is connected by narrow plastic tubing to the cut-off saw attachment and water flow produced by pressurising the tank by hand. However, this flow only lasts for a limited amount of time before the bottle is required to be pressurised again (normally a diamond tip blade will cut a paving slab in about one minute, equivalent to a single pressurisation) while frequent refilling of the bottle is also required. An alternative solution to this is a large water tank with a running pump to ensure supplies last an entire day.
Contractors need to plan for adequate water supplies at the start of the job. A significant volume of water may be needed depending upon the nature/duration of the work being undertaken. An appropriate supply must thus be considered at the planning stage and this can pose a problem in more remote locations. The effect of freezing temperatures on any water supply also needs to be born in mind.

16. Control Solutions Water Suppression has other advantages:
Extends the life of expensive diamond blades
Helps prevent build up of dust in the machine workings
Diamond blades are expensive (how much). Using water helps to significantly prolong their life and hence reduce costs.
Water suppression also helps prevent the build up of dust in the machine itself which will damage it in the long run. The photographs shows a cut-away section of a saw containing filters and this will get covered in dust if used without proper controls. Also an important point to raise with those servicing the machines such as hire shops.

17. Control Solutions Issues associated with water suppression use:
Marking the cut line
Slurry generation
Wet legs
Many workers mark the line of a cut with chalk which can often be washed off by the water supply. This can be overcome by using other more resilient materials such as wax crayons or a proprietary marker.
Water / dust ‘slurry’ is created. This may be a particular problem where the staining of porous material such as natural stone is an issue. However, in most instances careful positioning of the cutting area can eliminate this and it is often an excuse used by those who do not want to use water suppression.
Operators may 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.

18. Control Solutions On-Tool LEV is also an option
Ventilation extraction on power tools can be effective and is associated with a number of tools used for different tasks. This includes angles grinders, power saws, wall chasers and surface grinders / polishers. It has the additional benefits of being safe to use with electrical equipment and does not generate the slurry associated with water suppression. However, the efficiency of the extraction process is dependent upon a number of factors. Effective extraction can be achieved where straight lines or flat surfaces are being worked on, e.g. wall chasing or mortar removal. However, this effectiveness is limited where there are curves, bends or uneven surfaces being worked or where work is at the edge of the material. The same is true where the blade is not properly enclosed by a hood, guard or brushes and/ or the amount of air extracted is not sufficient. The more effective devices usually have the extraction hoods built into the tool as an integral part of its design.
On-tool exhaust ventilation should thus only be selected carefully and critically.
Note that equipment can be made cumbersome by such systems which can also be easily damaged. Effective maintenance procedures are thus also important

19. What about RPE Disposable (FFP3) Power Assisted PF = 20
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 for further information on 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.
Nuisance masks are not adequate, A FFP3 is required as a minimum. Should provide individual boxes for PPE
PF = 20

20. More information
Time to Clear the air – free leaflet
Time to clear the air! Using cut-off saws for cutting kerbs and flag paving – DVD
Free leaflet and Free DVD down load from HSE website