The control of substances hazardous to health regulations blasting using silica sand

OC 273/18

This OC provides guidance on the prohibition under Schedule 2 of the COSHH Regulations of the use of sand or other substance containing free silica for blasting. It also gives some advice on silica-free substitutes.


1 The inclusion of the prohibition in the COSHH Regulations Schedule 2, of item 2 was to enable the repeal of the Blasting (Castings and Other Articles) Special Regulations 1949. Effectively the latter Regulations prohibited the use of sand or other substance containing free silica for the blasting of articles. However, the application of the definition used in Schedule 2 requires some interpretation.

2 The use of non-silica grits as substitutes is accepted industrial practice, although they themselves can also pose a risk to health depending on their composition.



3 The Control of Substances Hazardous to Health 1999, reg.4(1) provides for specific prohibitions as listed in Schedule 2 which includes a prohibition on the use of sand or other substance containing free silica for the blasting of articles.

4 Articles are widely defined and will include very large objects such as ships under repair or construction and other large fabrications (reference - Factories Act 1961 s.175). However, it does not apply to buildings, bridges or similar structures as they are not articles as determined by case law.

Silica sand and 'silica-free' sand

5 The use of allegedly 'silica-free' substitutes has frequently raised the question of what qualifies as 'silica-free'. In considering this, it should be appreciated that crystalline silica is a very commonly occurring substance in both the natural (rocks and soil) and artificial (mainly construction materials) environments. It is found in many extracted mineral substances as a main or trace component and may also arise from contamination at later stages of treatment and processing. Consequently many of these may not be entirely silica-free. The COSHH regulations do not define a concentration at which a substance is regarded as silica free, so it has been necessary, in practice, to apply a pragmatic limit of 1%. If a substance contains 1% or more of free silica, it is subject to the prohibition.

6 This limit has not been scientifically established. However, where a substance contains less than 1% free silica it is more than likely that the general COSHH respirable airborne dust level of 4mg/m3(see COSHH reg.2(d)(ii), definition of 'substance hazardous to health',) will be exceeded well before the MEL for respirable crystalline silica is even approached. Therefore, compliance with the general dust limit would mean that there is unlikely to be any risk to health from exposure to silica arising from the use of such substances.

Wet blasting

7 The conditions of the prohibition stipulate that it applies where the jet of abrasive is 'propelled by a blast of compressed air or by steam or by a wheel' (see second footnote to Schedule 2). Wet blasting uses water in the jet but in many cases, it may still rely on the use of compressed air to create the necessary pressure. Although it is known that levels of respirable silica generated by wet blasting are many times lower than those created by dry blasting, the legal interpretation is that, where compressed air is used to propel a wet abrasive containing free silica for the purpose of blasting of articles as defined above, it is also subject to the prohibition. If it can be demonstrated that compressed air (or steam or a wheel) is not used then the process is not prohibited.

8 Wet blasting is commonly used with the cleaning of buildings and other fixed structures where the prohibition does not apply regardless of the means of propulsion. The use of substitute materials has proved effective in both the final surface achieved and in reducing overall dust levels, particularly respirable silica. Any decision, therefore, by the employer to use abrasive sand or other substance containing free silica in a wet process must be clearly justified in the COSHH assessment. Occasionally there may be situations where issues such as efficacy, cost and environmental pollution need to be considered in relation to the abrasive used.

9 Alternative abrasives have been successfully used for the wet blasting of ships. Ultra-high-pressure water jetting may also be used as an alternative method of surface cleaning.


10 A more restrictive interpretation of Schedule 2 could be advanced - that the prohibition only applies to articles that are themselves 'in any blasting apparatus'. Such an interpretation should be resisted.

Abrasive substitutes

11 There is a large range of substances available as substitute abrasives for silica sand, eg steel grit, specular haematite, copper slag, nickel slag, crushed glass, garnet, olivine. Some (eg garnet) may contain crystalline silica impurities, in which case they will be subject to the prohibition unless these amount to less than 1% of the total, but even if below this limit they may still be hazardous in some other way. Some (eg coal slag), like crystalline silica, can cause fibrosis of the lung while others may present other toxic hazards either arising from the main constituent of the substance itself (eg nickel in nickel slag) or impurities (eg arsenic in copper slag.)

12 Whatever alternative substances are used, the COSHH regulations require that the employer should properly assess the risks created by their use in blasting and identify and implement the necessary measures to control those risks.

Enforcement policy

13 If situations are found where there is blasting of articles as defined by COSHH schedule 2, item 2, with sand or other substance containing free silica at levels of 1% or greater, then inspectors should use their enforcement powers to ensure that this work does not continue. The following enforcement advice conforms to the Enforcement Management Model, operational version 2.0.

14 If the circumstances are such that there is evidence of a risk to health to either employees or the general public affected by the work, then the issue of a prohibition notice (PN) would be appropriate. However, if the employees are fully protected from the risk of inhalation of silica dust and no other persons are involved then an improvement notice (IN) would be appropriate. (It does not hold that simply because the activity is prohibited by Schedule 2 that this is in itself grounds to issue a PN.) In view of the longstanding requirement not to use silica sand and accepted industrial practice, inspectors encountering this activity should seriously consider prosecution.

15 A flow chart in the appendix encapsulates the enforcement policy.

Wet blasting

16 As indicated in para 7, wet blasting of 'articles', including ships under repair and construction, can fall within the terms of the prohibition and where it does, inspectors should take action accordingly. Where wet blasting of buildings or other fixed structures is being carried out, inspectors should approach it from the angle of routine COSHH enforcement, ensuring that the employer has properly considered substitution. The Construction Sector may be able to provide further guidance of industry practice.

Silica-free substitutes

17 Given the large number of silica free substitutes available and the variability of their composition, it is not feasible for HSE to state which are safer to use than others. The onus is on employers to assess the risks from any substitute and to implement controls as appropriate. Inspectors should use their enforcement powers to ensure that a suitable and sufficient assessment has been carried out. If there are any doubts about the suitability of the assessment inspectors should also consider enforcement action under COSHH reg.10 to ensure that any relevant OELs are complied with.


18 Employers will also need to assess the risks from exposure to substances hazardous to health which may arise from the materials comprising the article or structure which is being blasted, particularly lead paint (where the Control of Lead at Work Regulations 1998 will apply). Inspectors may need to consider enforcement where this is not the case.

Cancellation of instructions

19 OC 273/8 - cancel and destroy

Date first issued: 21 November 2001
Disc: j:\editors\intranet\ocfiles\200-299\273_18.lwp

Updated 2020-08-04