When the risk of tank failure is not as likely or when it would not cause extensive damage, the bunding may be designed to merely contain small leaks from hoses and valves. This bunding may not be able to contain the entire volume of the tank. Plastic and steel are used, but another common method is making a hump or lip around the perimeter of a concrete floor. Some bunding is temporary, such as short-term chemical storage in the field. A hump or slope type bunding is helpful when vehicles need access to the area. There is also a type of bunding that compresses when a vehicle passes over and expands once it has passed.