Maybe some context is missing. I might guess that the customer intended a minimum fs of 6 for bursting against the design pressure.
Actually, I might ask the customer to explain in more detail what he means, because it doesn't _say_ minimum. That's sort of implied by 'factor of safety', but lawyers could argue it either way.
To demonstrate compliance with a strict interpretation of what's written might have you using foil tubing, and I don't know where to get it or how to terminate it.
How many lawyers does your customer currently own or rent?
Mike Halloran
Pembroke Pines, FL, USA