The problem with underground fuel tanks is that they are out of sight and often out of mind. A leak detector, however, is above ground and normally the only visible part of the system, even if it has been stuffed into a cupboard somewhere in the back office or corridor.
By fully understanding the different types of leak detector, it is possible to gain an understanding of the type of tank it is monitoring, as well as the level of risk the system possibly poses.
There is an EN standard for leak detectors, but it is not a mandatory standard, so in terms of the policing of leak detectors, they fall into a bit of a grey area. It should not be assumed, therefore, that all leak detectors are the same. There are many leak detectors in the UK that do not meet the EN standard.
Cost is a major factor. Many of the non-compliant leak detectors in place in the UK market, were selected primarily because they were cheaper. It is not an insignificant cost difference either. For tank-lining systems, the cost difference between compliant and non-compliant could be as much as £10,000 per site. You need to know what you are buying!
There are many variables when it comes to leak detectors. Under- or over-pressure systems, different levels of vacuum/under-pressure depending on the skin type, static or top-up systems and how many connections there are into the ‘interstitial space’ (interstitial space is basically the gap between the two skins).
There are a few key points, that will aid your understanding of the different types of leak detector.
Point 1: over-pressure is generally better than under-pressure. This is because an over-pressure system pushes out air from the interstitial space when a leak forms. This will generally prevent either ground water from getting into the interstitial space in the event of an outer skin failure, or fuel getting into the interstitial space in the event of an inner skin failure. As long as the leak is not too big, the over pressure leak detector, will have a built-in pump, to keep generating over-pressure while the detector is in alarm.
Point 2: to use an over-pressure leak detector, the tank skins must be strong enough to be subjected to the force of over-pressure, without collapsing. This rules out nearly all types of tank lining, other than structural systems. (Eurotank’s Lifeliner is strong enough to be monitored using over-pressure, for example.)
Point 3: Having a top-up system on the leak detector is generally regarded as best practice as any long-term permeation or micro leaks in leak detector pipework can be overcome by the system topping up ‘now and again’. Static systems (those without top-up pumps) will eventually need to be topped up if installed for 10, 15 or 20 years.
Point 4: For vacuum systems, knowing the vacuum level in the interstitial is important when assessing if the system is compliant with the EN standard. For example, if the vacuum level is around 100mb, there should be two connections into the interstitial, one in the top of the interstice and one that goes to the bottom of the interstice. If there is only one port into the interstice, then the vacuum level should be much higher at around 400mb.
Point 5: It is a very good idea to connect your leak detector to your tank gauge so that it can be remotely monitored. This is generally because history has proven that very often the loud or irritating noise a leak detector makes can be easily fixed by taking the fuse out of the spur it is connected to, or covering over the sounder etc. In a retail environment, relying on the site staff to react to alarms and report them is not 100% effective, particularly if there is a history of them going on and off over periods of time.
In summary, leak detectors tell a story and can either provide great confidence in the system they are monitoring or great concern. Like so many things in this industry, the devil is very much in the detail.