Ex. We have a system demand of 65 psi. Available water is 100psi. We have a safety factor of 35psi.
If we say "how much "extra" water is there over the demand, I'd divide 35/65 and have a safety factor of 53.8%
If we say "How much of the "extra water" is in relation to the supply, I'd divide 35/100 and ahve a safety factor of 35%.
Just curious, as we have some AHJ's that mandate (10%) but don't stipulate what that is off of. It's cut and dry when your required to decrease the supply by 10%, or an AHJ states 10psi, but when a generic 10% is the altered code, we have a little debate in the office right now.