For those of you who are unaware, there is a certified safe and legal option for using and refilling and transporting one pound propane tanks. For now there is only one company offering this to the public. It is becoming widely available in major chain stores and on-line.
It's called the Flame King Refill System.
http://www.flameking.com/products/1lb-refillable.htmlhttps://youtu.be/AKvxlhiKfFAManual.
http://www.flameking.com/media/wysiwyg/Training_Manual_for_1_lb_cylinder_fillers.pdf The tanks are designed to blow mist out of a bleeder gauge valve to let you know when the tank is at the 80% full mark as you fill them. The remaining 20% is for expansion of the gas. This removes guessing how much is in it and is how much gas they are supposed to hold.
Please wear thick gloves to protect your skin and wear eye protection.
Always refill away from buildings and open flame or sparks.
After filling a tank, try to hold the 1 pound tank to refill valve tight until the valve is completely unscrewed to help prevent gas leaking at that connection.
Many of us have switched over to this system for obvious reasons, the number one reason is safety.
The disposable tanks (D.O.T. 39) are illegal to refill and also to transport after refilling.
Some concerns about their recall in the past are noted here:
Incidents/Injuries: The firm has received two reports of the connecting valve starting to unscrew from the cylinder. No injuries have been reported.
Flame King 16.4 oz. green 000001 through 020800
http://www.flameking.com/recall