Jet A1 and heating oil have some similar properties but are different products. In the UK they do not come from the same tank.
Every last litre of Jet A1 (F-35) supplied in the UK is traceable back the the refinery from which it came .... and beyond that it can be traced to the crude from which it was refined.
Jet A1 specification can be found in the document Defstan 91 - 91, the current version is revision 7 which is effective from Feb of this 2011.
Jet A1 with FSII (F34) is not produced at refineries, it is produced when Jet A1 has certain additional additives present; these additives can be added in the distribution chain, the first point they can be added is when Jet A1 is loaded onto road tankers at distribution depots. The next option is an airfield fuel bowser which can add FSII as Jet A1 is delivered to an aircraft. The last option is to dispense FSII from an aerosol directly into aircraft tanks at the same time Jet A1 is being delivered.
In recent times the content of FSII from aerosols has been identified as being a health hazard so you may find the refuelling operatives are no longer willing to assist with the use of these products.
The delivery documentation which accompanies a fuel delivery is a legal document, under normal circumstances no one gives a jot about it. However following an incident this document can become extremely significant, it clearly documents the precise standard of the the fuel supplied.
This is the point where the difference between Jet A1 and 'any alternative' fuel would become evident. The quality control systems applied to Jet A1 up to the point where it is delivered to the airfield are extremely demanding, on airfield they should also be demanding to the the minimum requirements of CAP 748. However you should expect to find the fuel system operator is able to demonstrate that they meet/exceed these requirements.
The use of alternative fuels is entirely a matter for the aircraft operator themselves. The powerplant manufacturer will have the final say on what is (and is not acceptable). I know of a recent 'misfuelling' incident where Avgas was delivered into a turboprop aircraft. The aircraft was eventually allowed to fly with a known mix of Jet A1 and Avgas; this was recorded in the tech-log and certain additional maintenance requirements were made within a particular number of flying hours after the incident.
Last edited by avturboy; 22nd Aug 2011 at 00:43.