Just thought I would post here. I troll and read quite a lot, but many years since I have even thought the need to show my opinion.
I used to work at a site every weekend, and always had a butterfly in my stomach when some new marshal tried to fill a tank. Having played for many years I always felt comfortable, and as our system was installed by HPAC, they also took the time to show us correctly how to fill the bottles. The bottles we used on site were steel bottles.
On a side note - I do a lot with modified engines, not so much diesel, but have touched upon some of the older style diesel manual injection. They have something called 'runaway engines' where they self fuel - turbo side seals break down and the engine will fuel it self from very thin (very hot) engine oil.
Why is this relevant? Well every time you clean a fill nipple, be it with a bit of WD40 or what ever choice of lubricant - you're filling an enclosed cylinder with highly compressed gas. You're also adding a bit of fuel (in the form of a thin oil, eg WD40). Sites also use penetrating oil to clean the air lines - if not cleaned out properly - you're just forcing fuel in to your tank.
Go back to the diesel engine - it is a sealed cylinder, with a mix of Air and Fuel, which gets put under massive compression, the fuel doesn't require a spark to combust (side note: which is why diesels don't back fire). Now take a step back and look at your own fill bottle. Diesel loves to combust with warm air. Ever filled your tank and thought "this tanks bloody hot (well warm)"?...
Ok on a site it is on a much larger scale (Weekends where we would have 300+ people each day weren't uncommon) - a lot more dirt in the fill nipples, a lot more frequent cleaning of taps and fill lines.
There were points where we were shaking the bottles to listen for debree, and oil, inside. As the gun tech for the site I would commonly open up the bottles (by removing the grub screws and unscrewing the regulator) and actually see what falls out. Lets say I 'cleaned' 10 bottles a day for example, using this method. Of the 10, 8 would have substantial mud and crud, 2 would have ample amounts of oil - now I am talking about 20-30 ml. lets add in to the equation the damage which all site bottles WILL have from being thrown around and bashing rocks on a field.
So... compromised container, high pressure air, moderate warmth and of course oil.
I have no legal qualification or accredited training to use the refill stations. Where did I stand in the eyes of the law? I would like to think my common sense approach to issues is why I am an engineer, and why I love engines so much, but in reality you have people playing the sport who are far less qualified (If we consider common sense as a qualification here) to even use a marker, let alone refill a 4500 pound-force per square inch bottle.
The only sensible ways to do it, which I can see, would be to employ persons at events and sites who have had sufficient training and given a sufficient knowledge base, or, require that all persons attending an organised event submit a filled in questionnaire regarding the fill station, the dangers and the key common sense problem solutions. (eg, nipple covers, use a non oil based penetrating fluid, listen for debree in bottle, keep bottles cool and without doubt a few hours brain storming will reveal lots more).
Been trying to find the video of that guy getting stabbed with the shards of CF after his wrapped bottle shat itself at an event 5 - 6 years ago.