Um..lifting's link to the exxon site highlights that jet A1 doesn't contain Fuel System Icing Inhibitor (FSII) as specified in Brit Mil standards for F34 which we put in our aircraft by choice.
It doesn't matter if we refuel at a civvy site and take Jet A1 but we have to log it. Since Jet A has a freeze point of minus 40 deg C and Jet A-1 is minus 47, I don't suppose it is much of an issue for most helicopter operators, except in the Arctic circle.
It would be interesting to get a definitive answer to your question Nellycopter - we might all be surprised
