FAQs

When dealing with UXO hazards on UK sites, guidance issued by UK organisations such as CIRIA (Construction Industry Research Information Association) and IExpE (the Institute of Explosives Engineers) is most appropriate.

Whilst guidance issued by the International Mines Action Standards (IMAS) isn’t irrelevant, the names of the various organisations gives a clue to their background and relevance.

CIRIA and IExpE guidance details good practice that should be operated in the UK.  IMAS is more military style guidance offered worldwide.  If CIRIA and IExpE guidance was not available, then IMAS would be a good starting point, but currently CIRIA and IExpE guidance should be used within the UK.

UXO is an abbreviation for unexploded ordnance.  Whilst there is a formal definition, it typically includes all types of ordnance and components.  This contrasts with a UXB which is an abbreviation for unexploded bomb, i.e. typically large ordnance dropped from an aircraft.

More formal definitions of UXO consider its state and condition of arming, but the within the commercial sector, UXO is used to refer to any ordnance or ordnance components discovered, no matter what state they are in.

No.

Obviously you should call the emergency services if you find UXO in a busy public place.

But otherwise, consider whether its necessary to draw on valuable emergency services time and resource.  If you find something suspicious (e.g. in an excavation on a site), call a UXO specialist first.

It is highly likely that the item is not UXO, but the UXO specialist will be able to advise and in the very unlikely event it is necessary, they will advise if emergency services are required.

UXO specialists like Zetica can arrange for commercial explosive ordnance disposal (EOD) for you.  This follows guidance issued by the Institute of Explosives Engineers (IExpE), the MoD and the emergency services.  This offers significant advantages where a more discreet EOD operation is preferred, avoiding evacuating the public.

Remember that most UXO found in the UK is very unlikely to detonate on discovery and is perfectly safe if you leave it alone.  It is important to call a UXO specialist as soon as possible.

Ideally your UXO specialist will have experts in their fields, including:

• For UXO desk studies and risk assessments, you would expect to see experienced risk assessors typically degree qualified in relevant subjects such as military history and risk assessment. The addition of experts in civil engineering, geology, explosives/ordnance, contaminated land or other related disciplines is important.
• For UXO detection, you would expect to see a competent geophysics specialist that is at least educated to degree-level in geophysics or a similar field. It is important to have a geophysicist or a person trained to understand geophysical techniques and the key aspects of UXO detection.
• For Explosive Ordnance Clearance (EOC) and Disposal (EOD), a competent engineer is defined within guidance provided by the UK’s Institute of Explosives Engineers (IExpE). You should expect a certified qualification from either a military or specialist trainer in EOC or EOD.  Training alone does not make an EOC/EOD engineer competent, experience is critical. There are 4 levels of competency:
  • Level 1 is acceptable for a person to be part of a team, but not to work alone. Levels 2, 3 and 4 are most appropriate for EOD.
  • All levels should be capable (subject to assessment) of conducting instrument searches (UXO detection). This approach does not require geophysics specialists.

You may be told that all UXO is likely to detonate or that it is common for fuzes to become more sensitive with age.  In practice, this is not supported by the evidence or science.  UXO you are most likely to find in the UK is very unlikely to detonate upon first encounter.

It is still important to treat any potential UXO with respect and not to disturb it further, and immediately contact a UXO specialist.

In theory yes.  In practice, UXO most likely to be discovered in the UK is very unlikely to detonate spontaneously.

In northern Europe, some of the fuzing mechanisms in Allied bombs have been known to cause a spontaneous detonation.  This is, however, incredibly rare.

UXO is regularly found in the UK, probably on a daily basis.  This reflects the long history of military activity and the subsequent development of areas where this activity took place.

There are many military and commercial UXO clearance tasks happening across the UK every day.

Our website tracks some of the more notable finds that make the media, but often if the disposal task is done well, it will go unnoticed!

Not since probably the late 1940s.  Records are sparse on this and the UK Government doesn’t seem to hold any formal records.

It reflects the fact that typical UXO found in the UK are very unlikely to detonate on first encounter and also diligence of those in construction who tend to take appropriate action when something suspicious is found.

The situation is very different in other countries like Germany, where WWII bombs dropped by the Allied forces are more likely to detonate and have killed many in construction since WWII.

UXB could be present at depths of up to 35m in the UK.  Actual depth will depend on geology where denser soils will limit the depth of bomb penetration.  More typically, UXB in the UK are found within 10m of ground level.

NO! – There is no such licence.

Some UXO specialists state that their firearms licences are Home Office approval for EOD.  This is wrong!

There isn’t specific legislation. However, legislation such as the Health and Safety at Work Act and the Construction Design Management (CDM) regulations require developers to ensure a safe working environment.

If UXO is a reasonably foreseeable hazard, then it should be addressed.  Often, this will simply be a preliminary UXO risk assessment which you can undertake yourself or if you prefer, ask a UXO specialist.  Zetica offer this service for free (pre-desk study assessment), others charge a small fee.

High explosives within UXB are typically very stable and do not significantly degrade or become more sensitive with age.  Some primary explosives used in fuzing mechanisms can degrade to sensitive compounds depending on conditions.  In practice these compounds do not survive long and further degrade to insensitive compounds.

You may hear rumours like ‘it’s common for fuzes to become more sensitive with age’.  This is not supported by the science.

The potential for an accidental detonation when UXO is first encountered remains very unlikely in the UK.  This is verified by the 1,000s of UXO found each year and the absence of accidental detonations.

That said, any suspected UXO should be treated with respect and not moved or disturbed.  A UXO specialist should be called immediately.

No, in practice WWII bombs are probably the least commonly found UXO in the UK.

UXO specialists like Zetica deal with thousands of UXO a year, with the overwhelming majority comprising British Land Service Ammunition (LSA) reflective of the country’s long military history. Ignoring small arms ammunition (e.g. bullets) which can be found in vast quantities, most commonly found UXO are mortars, medium calibre projectiles (small shells) and grenades, among other items.

UXB tend to make news headlines due to the disruption such finds can cause.

Our news feed lists examples of UXO found and reported by media.

On some sites it isn’t low.  But you won’t know unless some assessment is made.

If you are developing a site, you are responsible for ensuring a safe working environment.  If a foreseeable hazard from UXO has been identified, you have the opportunity to take reasonable and proportionate steps to mitigate the risk.

Being prepared will keep you safe and keep costs low, as an unexpected UXO find can cause significant disruption, delays, and reworking.

In practice, a preliminary risk assessment may be sufficient and companies like Zetica offer this free of charge, with others providing a similar service for a small fee.

In the UK, abandoned bombs are those associated with credible records indicating they remain in the ground as UXB.  Typically, they were in locations difficult to access or despite credible records confirming their existence, they had not been located yet.  The list was maintained by the Ministry of Defence (MoD), but is no longer maintained.  Zetica has a copy of the original list, which is consulted for our risk assessments.

Abandoned bombs are not to be confused with UXB marked on historical maps and lists.  These have typically been removed or discredited.

Some UXO specialists prefer military terminology as it is familiar to them.  Others prefer terminology familiar to customers they work with.

For example, the term ‘risk assessment’ is more familiar to many, whereas ‘threat assessment’ is a more military derived term.

Inconsistent terminology and definitions are a problem and can be confusing for developers.  Asking your UXO specialist to use more appropriate wording for your industry is quite acceptable.  It is the UXO specialist’s responsibility to provide clarity to help your understanding.

With any hazard, appropriate risk mitigation should reduce the risk to as low as reasonably practicable (ALARP principle).  The same applies to UXO.

In some cases, despite all reasonable efforts, some risk may remain.  This may be due to the nature of the hazard, site conditions, or prohibitive costs.

In these instances, guidance as issued by the UKs’ Health & Safety Executive (Reducing risks, protecting people, 1999 and amendments), gives reassurance that provided the risk is tolerable, the development can continue.

It is important that you understand what this risk is.  Your UXO specialist should make this clear to you in any reports.  If the residual risk is not clear, ask!

No. In many respects, UXO is much easier to deal with than many other issues you might face when developing a site.

A good UXO specialist should be able to provide you with options to help make your site development a success.  It could be a simple strategy of avoidance, where some tweaking in the overall design/layout is enough, or other options that ensure you reduce the hazard to as low as reasonably practicable (ALARP).

If your UXO specialist immediately insists that all UXO must be removed, then seek a second opinion.

No. Just leave it exactly where it is, make sure no one else can disturb it and contact a UXO specialist.

Whilst you might think a bucket of water makes it safer, in practice you could be making things worse.  Some pyrotechnic compounds react with water and could smoke or catch fire.

So, the advice is to leave the item alone and get help from a UXO specialist.  The sooner you get help, the safer you will be.

No. Just leave it exactly where it is, make sure no one else can disturb it and contact a UXO specialist.

By taking it to a Police station you could be putting yourself at greater risk, putting anyone you pass at risk, and the occupants of the Police station at risk, all of which is unnecessary.

No.  Despite the name, a preliminary UXO risk assessment cannot assess the risk.  A preliminary UXO risk assessment simply won’t have sufficient information to properly understand the risk.

In fact, if you use a preliminary UXO risk assessment alone, you could put yourself at greater risk as you probably don’t have a good understanding of the hazard.

A preliminary UXO risk assessment should be used to identify whether a potential UXO hazard may exist and whether more detailed research is necessary (i.e. a detailed UXO risk assessment).

If you receive a preliminary UXO risk assessment that states a risk level, seek a second opinion.

In this situation, it’s a case of ‘you get what you pay for’.

It’s such a crucial stage of a project and is the foundation for what follows.  We always recommend, go for the best you can afford, as the more you spend on a UXO risk assessment the less you are likely to spend on any risk mitigation.

Cheaper UXO risk assessments tend to be based on limited site specific research, relying on more general records that result in uncertainty and conservative conclusions based on caution rather than facts. They often recommend extensive risk mitigation which may not be necessary.

Maybe.  It depends whether the work was able to remove UXO or confirm that UXO was not present.

In all situations, it’s important to understand exactly what was done and where, so you can be sure that the hazard has been removed.

No.  A UXO clearance certificate alone may not mean all UXO was removed.

Some UXO clearances can simply be a visual inspection, whilst others may be in-depth detailed surveys and investigations.

A certificate without detail of what works have been undertaken to achieve the clearance is unhelpful.

Ideally, you will have a report that states what UXO clearance work has been undertaken and what level of clearance has been achieved.

It is for this reason that today the issuing of clearance certificates is not considered good practice.

Most UXO found in the UK does not relate to WWI or WWII bombing. Typically, it is associated with activity such as military training and ordnance storage/disposal.  These activities are often concentrated in remote areas away from cities like London.

The potential to find unexploded bombs (UXB) is greater in cities like London. There is also a potential to find UXB away from cities due to bombing of strategically important targets like military airfields, or due to decoy sites designed to draw bombers away from their intended targets.

No.  It will depend on the type of UXO and the nature of your work, but in many cases you can simply avoid areas with a potential UXO hazard.  If left undisturbed, UXO does not typically present a risk.

Where potential hazardous UXO cannot be avoided, then you may need to investigate and remove it.

No. Bombing records are often incomplete and for confidence should be corroborated with other records where possible.

This is the same for any UXO hazard, where a single source of information should not be relied upon to provide a confident assessment of the potential UXO risk.

No. The UXO risk relates to the amount of bombing, and does not change based on whether someone was there during the bombing.

The uncertainty of the hazard level may be greater as no person was making records of bombs falling, but other sources of information should be consulted (e.g. aerial photographs) in order to provide a reasonable assessment of the density of bombing.

The UXO specialist should be able to provide a good estimate of the risk of UXB being present from additional records and comparison with surrounding areas where records may be available.

In an area of generally low bombing density, the risk of a UXB being present should not increase just because no one was watching.

There isn’t a standard definition of low, moderate and high UXO risk levels, but your UXO specialist should define the levels within their reports.  Without these definitions, it is impossible to tell whether the risk mitigation recommended is proportionate to the risk.

Zetica defines the main UXO risk levels as follows:

Very Low – There is positive evidence that UXO is not present, e.g. through physical constraints or removal.

Low – There is no positive evidence that UXO is present, but its occurrence cannot be totally discounted.

Moderate – There is positive evidence that ordnance was present or that other uncharted ordnance may be present as UXO.

High – There is positive evidence that UXO is present.

Very High – As high, but requires immediate or special attention due to the potential hazard.

No. We do often see risk assessments that cite the number of risk assessments previously undertaken in an area as a risk factor.  This is most likely just reflective of the level of development in an area.

Typically, yes.  Although the risk will depend on your proposed activity and the method and scope of UXO clearance undertaken.  You will need to assess the effectiveness of the UXO clearance in removing the hazard for your works.

No.  It is recommended that more than one source of information is sought so that details can be corroborated.  This will also identify any database inaccuracies.

Corroboration of records is critical to have confidence in understanding the potential UXO hazard on a site.

Yes. Most online risk maps relate to WWII bombing only.  A preliminary UXO risk assessment should be undertaken that addresses other potential sources of UXO (e.g. military activity).  This can be undertaken by yourself, or you can approach a UXO specialist to assist.  Some UXO specialists provide this service free of charge, others charge a small fee.

Evaluation of the geophysical data by a geophysics specialist, including modelling where appropriate, can provide an indication of whether a distinct anomaly is potentially UXO.  This, combined with common-sense assessment in context of the location (e.g. depth and size of the anomaly), and anticipated UXO on the site can provide further confidence in the assessment.

It is important that this potential is properly communicated and at no point should an anomaly be called a UXO.  In most cases, the probability is that the anomaly is not UXO.  Whilst some preparation for the investigation of an anomaly is prudent, mobilising an Explosive Ordnance Disposal (EOD) team in advance is unwarranted.

This will depend on the anticipated UXO anticipated, its likely depth, proposed works at risk and site conditions.

Shallow UXO detection – Typically, a non-intrusive (surface based) geophysical survey is appropriate to detect shallow-buried UXO. Magnetic techniques are appropriate for ferrous metal (e.g. steel cased) and electromagnetic techniques for non-ferrous (e.g. aluminium cased).

Deep UXO detection – Intrusive surveys using a magnetometer advanced into the ground by drilling  is appropriate for detecting UXO such as UXB at depth. Drilling techniques are typically either cone penetration testing (CPT) based (MagCone) or drilling-based techniques (MagDrill).  The latter is more suited to denser ground.   Both use magnetometers for ferrous UXO detection (i.e. UXB).  If other UXO are anticipated, a repeated shallow UXO detection survey at ~1-2m depth intervals may be required.

A UXO specialist should be able to provide an appropriate survey design, considering the factors above.

Most probably not and it’s important that this is communicated clearly.  Evaluation of the geophysical data by a geophysics specialist, including modelling where appropriate, can provide an indication of whether an anomaly is potentially UXB.  This, combined with some common-sense assessment in context of the location (e.g. depth and size of the anomaly), and anticipated UXB type can provide further confidence in the assessment.

To assess the anomaly, it is important that the data is saved so that it can be assessed as a back-office exercise.  We are often asked to investigate when a UXO specialist has detected an anomaly within a borehole using a magnetometer but has failed to record the data.  This can result in a lot of time and money being spent locating and identifying an anomaly that turns out to be nothing significant.

It is important that this potential is properly communicated and at no point should an anomaly be called a UXB.  In most cases, the probability is that the anomaly is not UXB.  Whilst some preparation for the investigation of an anomaly is prudent, mobilising an Explosive Ordnance Disposal (EOD) team in advance is unwarranted.

No.  Where possible, you can avoid anomalies.  Where avoidance is not possible, then investigation is required if you want confidence of understanding what the anomalies are.  Focusing on the higher priority targets first, the results from this will help inform whether investigating the others is necessary.

Prioritising anomalies can be done by evaluating the geophysical data with some common-sense assessment in context of the location (e.g. depth and size of the anomaly) and anticipated UXO.

If your UXO specialist has not tried to discriminate or prioritise anomalies for investigation, ask them to do so, or ask another specialist to assist.  It could save you a lot of time and money.

Your risk tolerance, and the level of clearance required, should also be considered.

If the Made Ground is comprised of reworked natural materials without significant metal/ferrous content, bomb detection may be possible.

If Made Ground has significant metal/ferrous content, this is likely to reduce UXO detectability, potentially masking the signature of a bomb.

Because detection depths and radii vary with changing site conditions.  The actual detection limits achieved should be assessed for each site.

If a UXO specialist reports the same detection depth and radii, for every site, it may indicate that they are not actually assessing the limits of detection, rather relying on the maximum theoretical capability of the survey equipment. This could mean that parts of the site have not been properly cleared of UXO.

This depends on the depth of your work and anticipated depth of the UXO.  You only need to achieve UXO clearance to the maximum depth of your works or maximum likely depth of UXO, whichever comes first.

It is important to note that the anticipated depth of the UXO is refined based on actual site conditions encountered. For example, geological variations across a site may mean that bombs could penetrate deeper in one area compared to another. UXO clearance may therefore be required to different depths on the same site.

Generally significant risk mitigation for UXO is not necessary for a low risk.  Low risk is usually based on the potential to encounter UXO being no greater than any other similar area of the UK (background risk).

You may employ some mitigation where your risk tolerance is low.  This is common for sites such as nuclear establishments where even a low risk of encountering UXO unexpectedly is not welcomed.

UXO awareness briefings/toolbox talks are prudent for all risk levels, ensuring staff take appropriate action in the unlikely event of a suspect find.

No. The UXO specialist undertaking the MagDrill should be collecting the geophysical data so that the anomaly can be assessed back-office by a geophysics specialist. Often, this will enable the anomaly to be discounted as a potential bomb and the drilling can proceed.

If the anomaly models as a potential bomb, the borehole may need to be relocated. But it is important that the nature of the anomaly is properly communicated and at no point should an anomaly be called a UXB.

Of course, if geophysical data is not collected during the MagDrill works, such assessment is not possible, and the borehole may have to be abandoned.

The data should be shared with a geophysics specialist to further assess the anomaly. Often, this will enable the anomaly to be discounted as a potential bomb and the MagCone survey can proceed.

If an anomaly cannot be discounted as a bomb, the easiest approach is to redesign the pile layout to avoid the anomaly.

Only if the anomaly models as a bomb and the pile design cannot be changed, would an intrusive investigation of the anomaly be required.

It important that the nature of the anomaly is properly communicated and at no point should an anomaly be called a UXB until it visibly identified as such.

Yes.  The dynamics of a bomb hitting the ground and a MagCone probe pushing into the ground are very different.

As an example, a bomb travelling at terminal velocity will penetrate several metres into medium dense gravel, whereas a MagCone probe might easily refuse, particularly where larger cobbles are encountered.

Refusal of a MagCone probe does not mean that the location is clear of bombs.  You must make an assessment on the likely bomb penetration depth based on the geology encountered, then compare if the MagCone probe has reached that depth.

An alterative method (e.g. drilling-based MagDrill) may be required to achieve the required clearance depth.

The more common smaller bombs (50kg) are typically detected to a maximum depth of 2.0m.

The actual depth of detection will depend on the site conditions.  This can be verified by a geophysics specialist, by reviewing the data and assessing the levels of geophysical noise.

The effect of naturally occurring noise or noise from Made Ground or existing structures can be significant.  This can detrimentally affect the levels of detection for a site and can mask the location of a bomb.

Understanding where the detectability of a bomb is reduced is one of the most important aspects of any UXB survey.

This is a term applied to the background/interference picked up by UXO detection equipment.  This can be naturally occurring within soils (e.g. iron content) or from introduced materials (e.g. buried metal), or other sources such as overhead power lines.

The effect can mask the signal that may arise from a UXO.

Technically yes, but in practice it is not recommended for the UK.  The effectiveness of GPR would be highly variable, and is more likely to provide inconsistent and inconclusive results compared to UXO detection using magnetic and electromagnetic geophysical equipment.

No. Magnetometers only detect ferrous ordnance (e.g. steel cased).

Non-ferrous ordnance (e.g. aluminium smoke grenade) and some low ferrous ordnance will not be detected by a magnetometer.

Electromagnetic geophysical instruments are required where non-ferrous/low ferrous ordnance is anticipated.

Yes.  But it’s important that you have the whole report, and it provides a good understanding of what works were undertaken where and what was achieved.  This should include any limits of detection and any residual hazard.

It is generally impossible to guarantee that all UXO has been removed from a site based on non-intrusive or other similar survey approaches.  Guarantees are only possible where soil has been physically excavated/remove or cleaned (e.g. picking through it by hand).  This is rarely undertaken or necessary.

A residual risk will usually always exist, but this should be low.  A clearance report should provide recommendations on how to manage the residual risk.

A mapped survey involves the collection of geophysical data for back-office analysis and interpretation by a geophysics specialist.

A real-time survey or ‘instrument search’ involves an operative undertaking real-time UXO detection, rather like metal detecting.  There is no data collected and instead reliance is placed on the operative listening and observing readings from the instrument.

Wherever possible, a mapped survey is recommended as it provides greater safety and can reduce the number of holes being dug.

Safety is enhanced through improved detection by analysing the data and removing potential human error (e.g. someone may miss a target with an instrument).  Analysing data from a mapped survey increases the chance of detection of deeply buried large items that would otherwise not be apparent using an instrument in real-time.

Analysis of the data enables target discrimination and ranking, reducing the amount of intrusive investigation required.

EOC and EOD Engineer competencies are defined by the Institute of Explosives Engineers (IExpE).

EOC/EOD qualifications should be appropriate to the hazard and the ordnance most likely to be found. As a guide the following levels are appropriate:

Level 1 – Level One operators are competent to locate, identify and destroy under appropriate supervision, single items in-situ on which they have been specifically trained.

Level 2 – Level Two operators are competent to locate, identify, move, transport and destroy multiple items on which they have been specifically trained.

Level 3 – Level Three operators are competent to conduct render-safe procedures and final disposal of any type of explosive ordnance except for specialisations listed under Level 4.

Level 4. Level Four operators are competent to carry out specialist tasks in the following categories provided that they have the relevant training:

1. Disposal of specific Guided Weapons.
2. Demilitarisation of Explosives Ordnance.
3. Chemical, Biological, Radiological and Nuclear weapons.
4. Improvised Explosive Device Disposal.
5. Disposal of weapons with specific fuel hazards.
6. Logistic disposal.

If competent to do so, then yes.  In practice, UXO specialists will typically have a team comprising of experts in their field rather than all-rounders.

Some Explosive Ordnance Disposal (EOD) operatives are competent to undertake UXO detection surveys.  The in-depth analysis of data and interpretation is usually undertaken by a geophysics specialist.

Likewise, some EOD operatives may undertake historical research for UXO risk assessments. The in-depth assessment is usually undertaken by risk assessment specialists with EOD operatives input utilised when assessing the risk of particular ordnance.

UXO specialists should be able to demonstrate that they have personnel with a range of capabilities, with those personnel undertaking the works for which they have been specifically trained.

No. There is no requirement or benefit to have an Explosive Ordnance Clearance (EOD) Engineer present during MagCone UXB detection.

The MagCone operatives should be trained to view the data on a screen and recognise if an object is about to be struck and so probing needs to be halted.

Viewing the real-time data on the screen alone cannot provide clearance of a pile location.  The data needs to be recorded and then assessed by a geophysics specialist to confirm data quality and radius of detection.  You cannot do this by looking at data on the screen in a MagCone rig.

MagCone operations will not expose a UXB and so having an EOD Engineer on the rig simply adds cost.

No. CPT operators are trained in safely collecting geophysical data.  The CPT/MagCone operatives should be trained to view the data on a screen and recognise if an object is about to be struck and so probing needs to be halted.

They will contact the geophysics specialist if a suspect item is detected, or for anything they are not sure about.

CPT/MagCone operations will not expose a UXB and so having an EOD Engineer on the rig simply adds cost.