While there is no regulatory requirement for us to comply with FAR 23 (design standards for type certificated light aircraft), it does provide a useful benchmark. FAR 23.1183 requires each line carrying flammable fluids ahead of the firewall to be at least fire resistant (i.e. covered in fire sleeve), except for "vent and drain lines, and their fittings, whose failure will not result in, or add to, a fire hazard".
My interpretation of FAR 23.1183 is that lines going to fuel and oil pressure senders should be fire sleeved, but that drain lines from fuel pump, sniffle valve, etc do not. This makes sense as normally the drain lines would not have flammable fluid in them, but fuel and oil pressure lines would have fluid that could make a fire worse if they were to fail.
It is also interesting to read that FAR 23.1162 states "components, lines, and fittings ... located behind the engine-compartment firewall must be constructed of such materials and located at such distances from the firewall that they will not suffer damage sufficient to endanger the airplane if a portion of the engine side of the firewall is subjected to a flame temperature of not less than 2000 ?F for 15 minutes." FAA Advisory Circular 20-135 Powerplant Installation and Propulsion System Component Fire Protection Test Methods, Standards and Criteria expands on this by stating "use of aluminum alloy for any size line/fitting on either side of a firewall should be avoided". My aircraft doesn't meet this criteria, as I have an aluminum fuel line in the cockpit connecting to an aluminum fitting at the firewall. But I can see how a fire on the engine side of the firewall could cause this aluminum fitting or line to melt and thus make things even worse. If I were doing this again, knowing what I know now, I would probably use a steel fitting at the firewall, and perhaps a flexible hose with steel fittings connecting to it on the cockpit side.
Note that none of above are requirements for our aircraft. But, they do provide a useful benchmark as to best practices. The odds are hopefully very small that we will ever find ourselves in a situation where this would make a difference. But, against all odds, back in March, I found myself in a car that caught fire after an accident. My wife and I were lucky to escape the fire, but I would have preferred the car to be more fire resistant. If my aircraft ever develops a fire ahead of the firewall, I hope the fire will remain as small as possible until after I can get it on the ground and get out of the aircraft.