Question: In the photo I sent in you can clearly see the “A2” lettering on the side of the hose, along with a bunch of Lloyd’s approval numbers and such. My question has to do with the “A” letter designations.

Hose constantly occupied by fuel is rated different from vent or fuel-fill hose.

Hose constantly occupied by fuel is rated different from vent or fuel-fill hose.

I’ve heard that these have changed in their meaning over the last few years and I’ve also heard that the bar has been raised on the requirements. Can you clear the air on all of this? What does A2 vs. A1 mean for example?

Answer: You are correct. We covered this a while ago in What do the New Marine Fuel Hose Markings Mean, but it would be worth circling back again because this is still a fairly new topic, and not well understood. It’s especially important for owners who are considering replacing fuel hoses in used boats.

Things changed with these designators in 2012 when the EPA-mandated diurnal emissions requirements for gasoline fuel systems on boats went into full effect. Basically what happened as a result of the new regulations is that the permeation rate standard for marine fuel hoses was tightened up rather significantly. A new designation was established for fuel distribution hose that now requires a permeation rating maximum of 15 g/m²/24hrs (15 grams per square meter in 24 hours). This is the new maximum for what is designated “A1-15” hose.

Several things about this designator are important.  First, any fuel hose with an “A” designator is fire-rated based on USCG requirements and specifications. It is the only rating allowable for fuel hose used in gasoline engine room spaces. In terms of the permeation specification, the new EPA required 1-15 designators are required for fuel distribution hoses. The assumption here is that these hoses are constantly filled with fuel and therefore we need to have a much lower permeation rate to keep fuel vapor leakage into the atmosphere at an absolute minimum. “A2” labeled hose is also USCG fire-rated but has a much higher permeation rate specification of 300 g/m²/24 hrs. It is also allowable in engine room spaces but should only be used for either fill or vent hoses going to the fuel tank. Again, the assumption is that these hose sections are not constantly exposed to raw gasoline, so a higher permeation rate is OK. There is also an A1 designation with a 100 g/m²/24 hrs. rating that is actually getting a bit hard to locate as most boat builders are using either the A2 or A1-15 hoses.

To add to any confusion here, there is also “B” rated hose available that has similar permeation properties but no USCG fire rating. They should only be used in non-engine room compartments.

For details on fuel hoses in diesel-powered boats, see Diesel Fuel Hose Ratings Explained.