TIME TO CHEER UP

30 January 1998

TIME TO CHEER UP

YOUR DIESEL TANKS

The cost of a major diesel

spill can go way beyond the

value of lost product.

Richard Darlaston of national

supplier Butler Fuels brings

Andrew Pearce up to

date on current best

storage practice

WAS it Zeus himself who, to impress the local crumpet, could turn into any shape? Farm diesel tanks are a bit like that, only without the potential end result. Travelling around, youll see everything from old heating oil containers on rickety legs right up to proper-job installations.

If whatever is on your place holds diesel and keeps (most) of the wet out, is there much incentive to improve it? Until a tank gets so dodgy that the delivery driver refuses to jump out of his cab, you may think not.

But the crunch will come if someone backs into that tank or puts a tine through the side; if vandals strike, or a major leak springs. Then the cost of pollution clear-up will land squarely in the farmers lap, and theres the possibility of prosecution as well under – deep breath – the 1991 Control of Pollution (Silage, Slurry and Agricultural Fuel Oil) Regulations. So, suggests Richard Darlaston, the question is not so much "Why should I update?" as "Can I afford not to?"

When an old installation needs cheering up, the Environment Agencys leaflet PPG2 Above-ground Oil Storage Tanks, lays out current best practice. Its the document that potential prosecutors will look to after an incident, so is your best guide. Heres a digest.

The key thing after site choice (not within 10m of a watercourse) is bunding – using an external catchment big enough to hold the tanks contents, plus a margin. There are two ways to achieve a bunded tank; either by buying a double-skinned unit, or building a separate bund round a single-skinned one.

&#42 Double-skin…

On the face of it, a self-contained unit looks good. And if made from plastic it wont rot or rust, wont need painting and cant collect potentially polluted rainwater in its bund. Such tanks can be installed at any height for gravity feed, assuming the base is completely supported. And the cost premium over a single-skin steel tank (around 50%, or around £200 for a 2500-litre unit) stacks up very well against the expense of building the separate bund.

But the guidelines suggest a few cautions. The tank must offer total secondary confinement (some dont), with the outer shell holding at least 110% of the inner volume, ie 2750 litres in a 2500-litre unit. Any potential double-skinner must deal with overfilling (in a good separate-bund setup, spills are automatically contained), and there should some means to see tank content level. Pipework should pass through the top, not the sides, as seals here can leak. A polyethylene tank should meet OFS T100 construction standards.

&#42 …Or single?

If you prefer the single-skin tank plus separate bund route, the guidelines are quite specific.

&#8226 Start with a tank that meets BS 799 Part 5 (steel) or OFS T100 (plastic).

lCheck that its pipework is up to scratch. Look for a lockable 50mm threaded inlet line (for security and leak-proof tanker connection) and see that all outlet valves or cocks are lockable against vandals. Vent pipe(s) must be able to deliver overspill into the bund, not drop it on the tank top – see diagram.

&#8226 Knowing the tank volume, work out bund capacity; the minimum is 110% of tank size. In areas where high rainfall can add to potential spill volume, add extra.

&#8226 For easy maintenance access around the tank and to contain all pipework, allow at least 750mm (29.5in) between tank and bund walls. Having thus settled on bund length and width, work out wall height to give the required volume. Then add at least 250mm (9.8in) more to allow for wind-generated slop or fire-fighting foam. In gale-prone areas build higher.

&#8226 The bund itself can be made from masonry or concrete, always rendered where needed so fuel cant seep through and frost cant work away at joints. The Environment Agencys two leaflets on construction go into great detail (see Box), and following their advice produces a completely bomb-proof structure. But depending on the site, the circumstances and the builders skill, it may be possible to build a simpler but still effective bund.

&#8226 However, if you decide to go about the job, the structure must be able to hold fuel without seepage and be plenty strong enough to hold the calculated volume. Into one corner build in a pump-emptiable sump, and set a fall on the base so rainwater or small spillages drain to it.

&#8226 Its illegal to channel contaminated bund water into a drain or watercourse. A simple gravity separator lets water be drawn off from the lighter floating fuel for safe disposal.

&#8226 Bearing in mind the weight of a full storage tank, build decent multiple support piers and tie their tops together. Set pier heights to produce a fall to the tanks drain tap end, so any water collects here and cant pass out with fuel.

&#8226 Mark the tank with its capacity and product type, and put up a notice close by detailing emergency procedures.

&#42 Final steps

All plant lasts longer with a little maintenance, and fuel stores are no exception. Its just common sense stuff; keep steel tanks painted, draw off internal water regularly to keep valves safe from frost and machinery fuel systems clean. Check external pipework and connections for weeps, and bund structure for condition. After all, theres no point in having a bund if it leaks when most needed.

HOMEWORK

Chapter and verse on fuel storage are laid out in three Environment Agency leaflets. Call 0645-333111 and ask for

&#8226 PPG2: Above ground oil storage tanks.

&#8226 Concrete bunds for oil storage tanks.

&#8226 Masonry bunds for oil storage tanks.

All are free, as is an advisory visit.

Providing a reliable supply of clean fuel is the primary purpose of a farm fuel tank. But farmers also have a duty to make the tank safe, non-polluting and properly bunded..

IF THE WORST HAPPENS

If disaster strikes an unbunded tank, dont hang about. Cost will be minimised by calling the Environment Agencys Emergency Hotline (0800 80 70 60) for advice and local disposal company contacts. Prompt, responsible action is a good move.

These plastic tanks are self-bunded, each with one skin forming a bund around the other.

In this set-up, fuel is pumped to a delivery gun through a meter so volume used by individual machines can be tracked. Security comes from steel pipework, a lockable steel cabinet and the option of isolating the pumps electricity supply remotely.

Best practice for an externally bunded diesel tank. Note how falls are set, lockable pipework is used, and the way that the vent pipe empties overfill spillage into the bund.

A tank within a tank. Although providing enough bund volume, this unit has extraction pipework exiting low. Current best practice is to route all pipes through the top to keep the bund wall intact.

A common enough sight – an unbunded steel tank on slightly second-hand support piers: No problem until theres a major spillage. Brownie points are scored for the outlet valve lock, though.

Steel bunding is an alternative to rendered masonry or concrete. In this setup, the outlet pipe runs through a welded union plate in

the wall so the bund stays intact.