To assess the structural integrity of a fiberglass tank, the following criteria should be used: visual inspection for cracks and other signs of damage; measurements of wall thickness; pressure testing; and, if necessary, x-ray or ultrasound testing to detect any internal damage. Additionally, the tank should be checked for corrosion and any signs of chemical attack. Finally, the tank should be checked for any signs of structural fatigue, such as stress fractures or weakened areas.