I had some H5010 powder go bad earlier this year. I purchased four pounds of this powder second hand so I can't be sure how it was stored prior to me acquiring it (I'm guessing by the lot # that is was made in 1994), but I did check to make sure each bottle was sealed. I then stored it a trunk inside for just over a year. When I found the powder, it had been about four months or so since I last looked in the trunk and was a little surprised to say the least. The smell was very noticeable as I opened the trunk and it didn't take long to see where it was coming from. As you can see from the pics, one bottle was way gone and a second was going bad as well. The two on the right seemed alright and were still sealed, but I didn't want to take a chance on them as I figured 220 grs of bad powder in a 50 cal may not be too forgiving.
I was curious how the powder looked and after scraping was was left of the lid and seeing a small but visible green cloud dissipate, I found the powder was almost one solid lump that I had to break apart. I also wanted to see how this stuff would burn was surprised to find that the powder would barely smolder when held to direct flame. The other three bottles all seemed to have similar, normal burn rates.
As a side note, I had always read that powder made a good fertilizer, but if your powder looks as bad as the one in the pics, don't put it on any plants that you care about. My good intentions were not enough to keep my wife from being mad at me for killing some of her roses