The time limit for. shipping a POV is the same as for travel and HHG transportation limits (JTR Para 5366, POV. Transportation Time Limitation), 1 year from the date of retirement/separation with severance. pay or 180 days from the date of separation.
The envelope is the large bag that holds the helium gas. The envelope is generally cigar-shaped, for aerodynamic purposes, and made of a durable, airtight, lightweight fabric (polyester composites) that is much like the fabric of a space suit.
All helium tanks need to be secured; this is the renter's responsibility. Helium is a nontoxic, non flammable gas, however it is dangerous to breathe in the gas from the cylinder, or even from an inflated balloon.