Does your tank have an OPD?
We cannot fill your propane tank unless it has an Overfilling Prevention Device (OPD), which is part of new national fire and safety standards designed to make the use of propane even safer. The OPD is a safety feature that prevents small propane cylinders from being overfilled. After January 1, 2003, all propane cylinders 4 pounds to 40 pounds MUST be equipped with an OPD.
How can I tell if my cylinder has an OPD?
Most propane cylinders with OPDs have special triangular hand wheels with the words OPD imprinted. Some OPDs, however, were produced before the letters OPD were required on the valve handles and valve bodies. 
What can happen when a cylinder is overfilled?
An overfilled cylinder may not have enough space left if the liquid propane expands when exposed to warmer temperatures. This can cause an increase in cylinder pressure and create potentially hazardous conditions such as:
- The pressure relief valve may open, discharging propane from the cylinder.
- Propane liquid could enter the piping system, resulting in higher than normal pressure to appliances.