Because the sand is durable and resistant to external environment and is quite difficult to change the situation. Therefore, it does not affect the fifo and contains restricted areas.
Because sand is durable and resistant to the external environment and rather difficult to change. So fifo does not affect use and consists of a limited space.
Because the sand is durable and resistant to the external environment and quite to state change can be hard. So FIFO therefore does not affect the use and comprising an area is limited.