UXO DISPOSAL - HIGH ORDER, LOW ORDER, LOW YIELD...CONFUSED?
Article Written by Andy Ward
Marine EOD methods and processes - a simple explanation
Recent months have seen a flurry of tendering activity for new renewables projects including the East Anglia Hub, Sofia and Dogger Bank OWFs. All of these have to consider the risk posed by UXO and how this can be safely dealt with paying due regard to minimising any environmental disturbance.
A couple of well-thumbed references from CIRIA and the Carbon Trust give valuable advice as to how best to mitigate the UXO risk and most of this is a well-trodden path. Disposal of items of UXO on the seabed however, is not as simple as it once was.
Whilst it’s not rocket science, EOD tends to be more of an art than a science and the seasoned disposaleer will have a few tools in their toolbox.
First and foremost is the use of deliberate (not accidental – we’ll touch on that later) High Order disposal, otherwise known as detonation or blowing it up where it sits (or where you may have managed to move it to if required). This is a reasonably simple task and one which most former Royal Navy EOD operators are well versed in. This is the primary military skill, taught by the Royal Navy and others as the most expedient means of getting rid of sea-mines which may have been placed by an adversary and which are getting in the way of a military operation. Think sea-mines off Kuwait laid by Saddam Hussein’s forces to sink or damage coalition shipping. Detonating these seabed targets achieves the military aim of quickly re-opening sea-lines of communication. It’s not pretty or environmentally friendly but it works.
Until very recently this was also the “conventional” or favoured method of clearing historic munitions from the seabed arena which proved to be in the way of an offshore wind farm or interconnector. High Order disposal charges are quite big - usually in the order of 5kg – 10kg of High Explosive and are placed firmly against the target item, usually by ROV in deeper waters but also by diver in shallower water, with the aim of sympathetically detonating it when the EOD Supervisor tells it to. It normally works well but tends to leave a fair bit of metallic fragmentation on the seabed not to mention the big crater and significant noise damage to sea-life. A crater of 4 – 6m is not uncommon depending upon how big the target item was, and the noise from a single detonation can be extremely harmful to mammals up to 26km away.
To get around these particularly destructive and noisy events, the EOD Contractor (a good one, anyway) can offer Low Order options. After all, we are not engaged in warfighting or military operations so we will hopefully have a little more time and can be a little more scientific in our approach.
A Low Order procedure is where we try to avoid full detonation and be a bit more clever about it. Low Order procedures are explosive means of making the item safe and can range from cutting the item open to knocking off the base plate to deflagrating (rapid, internal burn) and many other variations on the same theme. The Vulcan family of EOD tools offers (amongst other things) Low Order Deflagration whereby a low-density incendiary material is explosively injected into the target to ignite the explosive fill which then burns very rapidly. The pressure built up by the burning fill then bursts open the casing at which point the surrounding water quenches the burn – simples! The nice thing here is that only a hundred grams (or less) is required in the disposal tool so it’s very quiet and the effect on marine life is significantly reduced.
It is a tried and tested procedure having been used successfully thousands of times in military applications all over the globe. We need to consider a few other issues such as making sure that the internal components (fuzes, booster, primers etc) are safe and there are ways of doing this but probably the subject of the next blog.
It is no surprise that the days of routine High Order detonation are now numbered. Environmental awareness means we now demand capabilities which do not adversely affect our marine seascape in the name of offshore construction. EOD companies are looking at alternative techniques to bring to the market and Low Order processes are in the ascendancy.
So, let’s look at the 3rd possible option; the so called ‘Low Yield Neutralisation’. By the way, the term ‘Yield’ is generally used in the munitions industry to refer to the size and power of a nuclear weapon – we’d best not be confused over that one!
This time, the concept is to neutralise the UXO by injecting water into it at high velocity to break it open. This process, known on land as ‘Disruption’ is commonly used to counter Improvised Explosive Devices (Northern Ireland, Iraq, Afghanistan etc.) using small initiation charges such as blank shotgun shells. However, it is not used to counter conventional explosive ordnance (by conventional we mean military weapons of war such as aerial bombs, mines, torpedoes etc.) in the marine arena as the casing of these munitions is generally too thick. A ‘normal’ waterjet charge is really only looking to disrupt a fragile improvised device and without greatly increasing the amount of explosive force applied, this technique would not have enough power to penetrate the weapon casing and certainly not under water as the force of the water-jet (in water…) dissipates far too rapidly. Therefore, the only option is to use larger disposal charges. One of the current processes offered is two reciprocally placed, 750g explosive shaped-charges (directional explosive charges filled with a small amount of water) fired simultaneously. But, as we now know, the water shot probably won’t penetrate the casing so the disposal charge will either just push the ordnance several metres across the seabed or worse it will act (due to the high level of explosive charge) as a demolition charge and simply just detonate the target item due to the high energy output from the charges. Disruption may occur if the UXO is so badly degraded the force of the blast will further break it open, but this will still potentially leave the munition in a viable state requiring further EOD action before it is in a safe state to move. The other issue is the practicality of its delivery in challenging environmental conditions, particularly where the visibility is poor. Think of it as trying to position and fire two rifles at EXACTLY the same time at opposite ends of a target and expecting the water jets to enter at EXACTLY the same time – not even microseconds apart. Whilst this may be achievable in theory and potentially in a land situation, the dynamic operational marine environment will rarely be so forgiving. The ‘Low Yield’ (or neutralisation as it is also labelled) is possibly a viable system but certainly needs much more investigation before it is taken forward as a credible and reliable commercial EOD process.
And to put another misconception to bed, no procedure can ever be 100% guaranteed. Remember we said that EOD is an art and not a science? Most good operators can offer a high confidence level of the outcome – 95% possibly for some well proven systems but never, ever 100%. If someone offers this to you when disposing of a historic, possibly volatile item of ordnance, on an unstable seabed with nil or very poor visibility from a vessel pitching and rolling around, ask them how and why and where is their proof? Safe? Effective? Quiet?
So, in summary, there are 2 proven methodologies of disposing of hazardous (fuzed or armed) seabed ordnance; High Order (Detonation) or a Low Order technique. High Order is now seen as outdated, noisy, environmentally unfriendly and only to be used as a means of last resort so Low Order is the way ahead. Of these, Low Order deflagration is proven and following a series of Government trials to quantify the noise output regulators don’t even require noise abatement systems like bubble curtains to be employed. In the context of maritime UXO disposal, Low Order Deflagration is as mammal and fish friendly as you can currently get and with an ability to leave the seabed virtually undisturbed as it should be. What’s not to like?
If you have any questions about marine EOD procedures please contact EODEX;