Balance pipes are only permitted in diesel fuelled installations. The risks of
allowing them in petrol installations, where failure could lead to a bilge full of a
volatile fuel, are simply too great. In the event of the balance pipes failing, there
needs to be a way of shutting off the flow of fuel into the boat. This means that
any balance pipe between fuel tanks must be fitted with valves directly attached
to the tank. The valves must be leakproof and efficient.

Diesel fuelled boats manufactured before 16 June 1998, and fitted with a
balance pipe between close-coupled tanks (where there is insufficient space to fit
valves), are exempt from the requirement to fit valves directly attached to the tank.
If the connection between the fuel tanks is made of the same material as the
tanks and is also permanently connected by welded or brazed joints, it's treated
as an integral part of the tank and not as a balance pipe.

A fire started in the engine compartment after a jet of diesel fuel droplets sprayed over a hot exhaust pipe. Luckily the owner became aware of the fire and was able to put it out using a portable fire extinguisher. Worryingly the fire took place in a lock! [2.14]

Flexible hose, including armoured hose, can be used for balance pipes provided
the hose is manufactured to, at least, the fire resisting qualities of either BS EN
ISO 7480, SAE J 1527 or DIN 4798 and a valve is fitted at both ends. [2.13]