DRE carries the leafield pressure gauge.
As noted, the amount of pressure to explode a seam varies so much. Construction, temperature, material, age, exposure, care, the list goes on and on. If the boat is drum tight and left in the sun it can certainly exceed its limits, whatever they may be.
2.5-3.5 pounds is usually a good number for most standard sized rafts to run at. The amount of pressure needed to make a tube hard is related to its diameter. The bigger the tube, the less pressure it needs to be hard. A good way to see this is on a cat tube. Next time you see a cat on the water, if you dont own one, push on the tube close to the tip and then push on it where the tube is fat. You will find that the tube will be much harder in the middle where the tube is big and very squeezable at the ends even though the whole tube is under the same pressure. On the water, i always use the palm test that I have used since i was a kid. I want the boat to give a little when i push my palm into it at the fat part of the tube or i dont feel comfortable. I am certain that todays boats and materials will take much higher pressure than the boats I grew up with, but i'm not ready to let go of the palm test. Pumping a boat to 4.8 lbs would scare the hell out of me if it was my boat. Obviously, it has worked fine for Carroth but i certainly wouldn't recommend it. I did look at a Saturn i had in the shop today and it said max pressure 5.8 lbs. Keep in mind I am doing seam work on that saturn. I pump my boats up according to the palm test in the morning and rarely bleed air out during the day. I have a pressure gauge at the shop but it rarely gets used. Bottom line is, if the thing is drum tight in the morning and it sun bakes all day, especially on land, don't be surprised if you burst a seam. If you pump it drum tight in Denver and drive over Vail pass, don't be surprised if you burst a seam. I think that most rafts are very forgiving but common sense goes a long way. If you want to run it tighter than the palm test, run it just where it wont take a palm anymore, stop pumping and you should be fine. I have sat on rafts that just feel hard on my ass. If a rubber raft feels like you are sitting on a board, it might be a little tight. By all means, test until your hearts content, pump away until you are blue in the face and then click on my signature below to set up an appt.