Where Rn is the accessible slip obstruction, µ is the mean slip coefficient for Class An or B surfaces as material and as follows or as controlled by tests:
• For Class A surfaces (unpainted clean factory scale steel surfaces or surfaces with Class A coatings on impact cleaned steel or hot-plunged electrifies and roughened surfaces), µ=0.30.
• For Class B Surfaces (unpainted impact cleaned steel surfaces or surfaces with Class B coatings on impact cleaned steel), µ=0.50.
