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CMRA – Coal Mining Risk Assessment. Water flush drilling is safest say Coal Authority.

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CMRACoal mining risk assessment. Water flush drilling is safest say Coal Authority.

Let Geoinvestigate quote for your next Coal mining risk assessment or CMRA. Because at Geoinvestigate we have our own coal drilling and probing rigs we can provide cheaper quotes than other companies. Furthermore, our drill rigs use the safest water flush drilling system, as recommended by the UK Coal Authority.

So why do CA drilling licenses and permits allow the use of anything else but water?

Under the Coal Authority’s Contract CA18/02295 for small bore exploratory drilling works up to 160 drilling jobs have been carried out each year over the past 5 year contract period across the country, each with differing geological conditions and differing gas risks. Though the jobs and geohazards have been different what has always remained the same was the CAs insistence that only water flush was used for drilling. During the same period as many if not more exploratory drillings have been carried out by others mostly under license from the CA but not necessarily using water but a range of other drill flushes including foam, air mist and even air.

So, why this seemingly major contradiction between what the CA do on their own sites regarding safe drilling practice and their insistence of water flush only and the choice of flush they allow others to use on drill sites licensed by the CA?

Are the public not entitled to expect the same level of safety and risk minimisation irrespective of who is managing a coal drilling site?

Perhaps Geoinvestigate may have some answers to the apparent major contradiction which exists in safety standards between CA internally Managed drill sites and CA licensed externally operated drill sites.

Exploratory drilling for CMRA

Where there remains uncertainty about whether shallow coal mine workings exist beneath a site exploratory drilling is being resorted to more frequently (as part of the Coal mining risk assessment or CMRA) to provide a conclusive outcome. This is because drilling still remains the only dependable way of proving that a site is not underlain by cavities, holes or mine workings in the productive coal bearing regions of the UK or for that matter sink holes in the Karst Limestone and Chalk areas of northern and southern England.

The Coal Authority has on a yearly basis carried out up to 160 internally managed exploratory drilling jobs across the UK. Up till now most of this work has been done using extreme, small diameter long hole hand drilling techniques which because it uses only water flush has met the CAs stringent safety requirements ensuring minimal risk to public. However in response to safety issues raised by this technique this year by the Coal Authoritys CEO, this technique is gradually being withdrawn and is now relegated to a method of last resort being used only occasionally.

Seeing a gap in the market for safe, negligible risk, small diameter water flush drilling Geoinvestigate recently introduced their “state of the art” fully mechanised Microdrill. Microdrill small volume water injection system is currently the safest way of drilling shallow coal seams and coal mine workings.

Hazardous Gas Risk

The Coal Authority have for many years regarded the type of drill flush as being very important in ensuring the safe drilling of coal bearing strata where there may be a risk to the public from hazardous mine gases.

This is because the investigative drilling of shallow coal and abandoned coal mine workings carries with it the attendant risks of the cutting action of the drill bit igniting coal seams and starting underground fires or generating or releasing hazardous flammable or toxic gases such as methane and carbon monoxide.

These gases can be displaced by the injection of high volume drill flush causing gases to seep upward into the borehole or into occupied houses and buildings in the vicinity of the drill site. Hence Geoinvestigates new Microdrilling system uses only small volume water injection.


Gases released to surface by drilling


Gases forced to migrate by injection of drill flush


Coal Authority’s approach to safe drilling

CA publication : “Guidance on Managing the Risk of Hazardous Gases when Drilling or Piling near Coal” deals in Section 6 at length with the very real risks posed by various drill flushing mediums. The diagrams shown above are from this publication considered by some to be a “Code of practice” for coal and mine exploration and drilling.

The UK Coal Authority assesses this risk to be highest when drilling is carried with air flush and less when air misted water (atomised water) or foam is used. However the risk is considerably reduced becoming minimal or negligible when drilling is done using low volume displacement Water or Mud flush. For this reason the CAs preferred drilling medium for their own internally managed drilling/probing investigations is WATER ONLY, mud having messy environmental as well as health and safety issues. For this reason mud is rarely used.


Geoinvestigate’s new Microdrill, and Microdrills safe minimal risk water flush system


Recently Geoinvestigate came to fully appreciate just how particularly singular the CA are in their choice of drilling fluid and the stringent approach they have in this regard and to ensuring public safety during the planning and execution of small bore drilling works managed by themselves.

Earlier this year Coal Authority tender T28513 “Grouting and Drilling” the latter component also known as the exploratory small bore drilling works went out to public tender. In total over one year it may generate as many as 160 jobs across the country from Newcastle to Swansea. The contract runs for a 5 year period until 2020.

The tender specification was unequivocal stipulating WATER ONLY as the drill medium. In the tenderers open question session that followed the CAs online webinar presentation, the Authority responding to a question from Geoinvestigate about the possibility of using a range of drill fluid types including air misted water instructed all tenderers to strictly adhere to the tender specification and allow for WATER ONLY.

Subsequently the CAs specific requirement for Water flush was once again “hammered home” to Geoinvestigate during a demonstration of the company’s new Microdrill water flush system to the CA. This was attended by senior managers from the Authority including an expert SHE (Safety, Health and Environmental) Construction Coordinator and their Regional Project Manager the latter having many years of experience in the supervision of small bore investigative drilling works.

During the drilling demo Geoinvestigate were told in no uncertain terms by the CAs representatives attending site that day that “because of all the unknowns, imponderables and uncertainties with the ground and the public’s expectation that the CA (a quasi, non-government organisation or QUANGO) would be expected to take all reasonable measures necessary to minimise risk to the public from their drilling works. Consequently CA managed investigative drilling works could only be carried using WATER flush” and for this reason tender T28513 specified WATER only.

This is because water flush incurs the lowest risk whatever the site conditions may be and takes care of the all the unknowns, the imponderables the uncertainties as well as the unpredictable human factor.

Extract of Table 6.2.7 from CA document Guidance on Managing the Risk of Hazardous Gases when Drilling is provided below. Section 6deals both in detail and at length with the very real risks posed by various drill flushing mediums.


While other less hazardous “Situations” are described in the table only this category is shown here because in our opinion it most fairly describes the uncertainties of most first time exploratory drilling investigations where coal or mine workings may be encountered and why the CA insist on using water flush only for their exploratory works.

Essentially because of all the unknowns and possibilities the CA always appears to assume the worst case situation – in this way always minimising the risk to the public.

The CAs simple, straight forward and uncompromising approach to the use only of WATER flush for their own internally managed investigative drill sites (as stipulated recently in Tender T28513) is both highly rationale and very understandable. It is difficult to argue against, as it presents the safest approach to drilling ground where there may the possibility of encountering shallow coal or coal mine workings with the attendant uncertainties. Therefore an understandably cautious assessment is made of the coal geohazards resulting in a “High or unknown/undertermined hazardous gas risk” situation always being declared.

This situation is nearly always appropriate because in the early stages of Site investigation the Desk study and the subsequent license/permit application are necessarily often based wholly or in part on scant information or considered guesswork. Uncertainty continues right-up to the sinking the first deep exploratory Boreholes at which point it is usually only possible to establish the true nature of the gas risk at a site.

Because of delays in obtaining permits, perhaps arising from application backlogs at the CA, drilling can sometimes be carried out without first obtaining a permit adding extra risk if the encountered gas conditions are worse than expected and water flush is not being used to the drill holes.

This scenario is a very serious safety concern because drilling ahead of obtaining a permit does not allow the regulator to review the risk assessment for the drilling works and to request a change in the drill flush if this is what is required to ensure a safe outcome.

Even if some geotechnical information were to be available during the initial Desk study or permit application stages, often little is known conclusively about the actual ground conditions and the actual gas pathways that exist beneath the site. Furthermore even less is known about the conditions existing beneath the land surrounding the site though these external areas may be as important if not more critical than the site itself particularly if they are occupied by housing and the site itself was open space between buildings.

The uncertainty about the nature of the ground and gas conditions surrounding the drill site lends further weight to the argument in favour of always adopting a very cautious approach when choosing the drilling scenario using Table 6.2.7.

So while it would appear that on the one hand the CA operates a very stringent safety and risk minimisation policy towards their own internally managed drill sites a major safety contradiction or “double standard” exists in the way they license external drill sites through their permits application procedure.

Basically CA managed drill sites are safer because only water flush is allowed while externally operated licensed sites are less safe because a range of flush types is possible.

In their permit application procedure the CA rather than stipulating only water flush allow the applicant a choice of a flush types ranging from Water, Air Mist, Foam and Mud – the later rarely used in practice because of the environmental problems it causes.

CAs Drilling and Borehole Permit Application Procedure

Relevant extracts from the CAs permit application procedure are presented as follows

Proposed Works Section

In the proposed works section the CA gives the applicant a choice of drill flush type whereas in Coal Authority Tender T28513 there is no choice – only water flush. The choice of flushing medium is determined by a risk assessment based on a source – pathway – receptor model.

This risk assessment should also assess whether the proposed drilling works might cause hazardous mine gas to emanate off site and cause harm. Therefore it is implicit that the RA should also consider the possible ground conditions and gas hazards adjacent to the site.


General Risks Section

In the General Risks section of the permit application the CA insist that each and every applicant fully acknowledge that there is the potential for hazardous gas, fire and other risks to occur on each and every site. Understandably there is not a NO option “opt out” for the applicant to tick.


In the next section Geoinvestigate have attempted to interpret the possible mindset of the CA carrying out such a risk assessment as though they were an external body applying for a permit from the Authority for exploratory drilling works.

Geoinvestigates hypothetical interpretation of the assumptions that the Coal Authority might make. It is purely an imaginary exercise and does not in any way profess to be based on fact.

What Might a drilling or borehole risk assessment by the Coal Authority look like?

The assumption made is that the site is typical of the uncertainties of most UK sites with regard to the difficulty of predicting ground conditions in areas underlain by shallow productive coal bearing rocks with all the pathway possibilities and uncertainties that could exist not just within the site but also beneath the adjacent lands which are occupied by housing and for which there is little or no Desk study information. Therefore it could be a Coal mining risk assessment in Leeds, Newcastle, Bradford, or a multitude of urban localities anywhere across the UK.


Risk Assessment for choice of drill flush based on source – pathway – receptor model.


Source – YES shallow coal seams/possible shallow coal mine workings. Unknown or undetermined hazardous gas risk both within site and surrounding site.

Receptor – YES occupied residential both within site and adjacent to site

Site Pathway – UNKNOWN but possibly YES. Little data. Desk study indicates possible glacial clay with perhaps sand/gravel channels, with variable shallower and deeper rock head. Other possibilities include unidentified faults, deep variable fill, unidentified/unrecorded mine shafts or adits, deep pile foundations, vibro stone column foundations, basements.

External Pathway – UNKNOWN but Possibly Yes. No or little data on adjacent land which is occupied residential.

Outcome – Within this site and adjacent to it possible source – pathway – receptor models exists therefore the hazardous gas Situation is UNKNOWN or UNDETERMINED. A HIGH or HIGH to MEDIUM risk exists to the public should Air, Air Mist or Foam drill flushes be used.


Action – In accordance with the Coal Authorities Table 6.2.7 use WATER flush only to minimise risk to the public. Air flush, Air Mist and Foam are not acceptable. This decision is also in accordance with the CAs own stringent safety requirements for managing their own internal drilling works wherein only water flush being by far the safest drilling medium in all scenarios is specified as it was recently in the CAs exploratory drilling works Tender T28513.

It is clear from Geoinvestigate’s participation in CA Tender T28513 that the risk to the public from the drilling process is potentially always HIGHER on a site licensed by the CA to an external party and LOWER on a CA internally managed drill site. Such a major inconsistency in approach to site safety poses a very real safety risk to the public who would rightfully expect the CA to ensure the lowest level of risk in all situations irrespective of who is managing the drill site.

It is Geoinvestigate’s opinion that the drilling risk assessment should sensibly err on the side of caution thus allowing for unexpected but foreseeable variations in ground conditions, human error and negligence. Examples of the latter might be – knowingly or unknowingly ticking the wrong flush type box in the permit application, subsequently changing the flush type during drilling without first seeking the approval of the CA drilling without a permit or drilling with an invalid permit because the flush type being used is not that stated on the permit or any permit at all.

The mandatory requirement of using WATER FLUSH only when carrying out exploratory or fist time drilling works in suspected coal or coal workings would ensure the safest outcome in all these circumstances whether the conditions proved more hazardous than had been originally expected or errors were made in the permit application procedure or the wrong drill flush was used subsequently.


Geoinvestigate’s New Microdrill undergoing final tests

The option given by the CA of applying for retrospective or hindsight permit is of little use in the aftermath of an explosion or a serious hazardous gas incident which could happen if a less safe drill flush is used unbeknown to the CAs licensing desk.

This serious safety contradiction highlighted in this document between the HIGHER safety standards the CA sets itself and the lesser standards the Authority expects from others involved in similar exploratory drilling works needs to be questioned and resolved as quickly as possible.

This is because the public should at all times expect the highest levels of safety and risk minimisation by the CA whether the investigative drilling works are being managed under the direct supervision of the CA or are being operated externally by others under regulation and license from the CA.

If there is to be an exception why water flush is not to be used the applicant must give very good reasons why in this instance this should be accepted by the CA with the expectation that in most cases such a request will be rejected by the Authority.

An issue which touched upon again and which the CA needs to look at is the possibility that in making a license application the applicant ticks the water flush box, but either known or unbeknown to them the subsequent drilling work is carried out using higher risk flushing mediums such as air, mist or foam.

Perhaps the CA needs to consider regularly inspecting or spot checking licensed drill sites. If such safety monitoring is not possible this is yet another very good reason why in most cases only water flush should be specified in the CAs licensing of external permits.

From the simple arguments presented in the foregoing discussion the logical and obvious outcome is that the CA should specify WATER FLUSH only as the standard drill flush on all licenses obtained by external parties as it was specified in CA Tender T28513 for their own internally managed small drilling works.


Microdrills safe, negligible risk Water flush system At 12m drill penetrates coal

In due course it is Geoinvestigate’s intention to discuss this document with the CA and to request that they provide information on how they carry out source-pathway-receptor model risk assessments for their own internally managed drill sites.

Geoinvestigate will request the CAs assumptions on the ground conditions, pathways and gas hazards at each site and how in Tender 28513 which involves some 140 – 160 jobs per year all at different locations across the United Kingdom (each having a different set of geological conditions and gas risks) why the outcome is always the same namely WATER FLUSH only where the CA is directly responsible for the management of the drilling works.

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