Going in and chopping their heads off would work well and be quick and humane. I wouldn't want to be the one of the people doing that, but....those poor birds.
Yes, cervical dislocation is the most humane, but in no way is that an option for commercial flocks. You're not talking about a handful of birds. It is more in the neighborhood of 40,000 birds in each barn. There were 900,000 turkeys culled in Minnesota alone.
http://www.startribune.com/lifestyle/health/299450701.html
5 million chickens were culled on one farm in Iowa. There is no way to chop the heads off of 5,300,000 birds.
http://www.npr.org/blogs/thetwo-way...llion-chickens-in-effort-to-contain-avian-flu
There isn't a good method at present to depopulate caged hens which is what has to be done in the last story.
The foam is only used for floor birds because only one worker is required to enter the building. That worker doesn't need to handle birds so there's no threat to the integrity of their PPE. It suppresses the dust and can be impregnated with anti-microbial agents.
For caged hens foam can't be used because it doesn't penetrate the cage well, nor does it hold it's consistency in the cage.
Utilizing cervical dislocation, there are more than just a few problems.
Workers need training and skill is necessary to kill birds humanely.
Large numbers of people would be required to depopulate a house quickly.
Fatigue would be a problem if a person must kill a large number of birds in a day.
A person fully dressed in PPE could become overheated and be tempted to remove parts of it for the sake of comfort.
Constantly reaching into cages grabbing struggling hens would create chances for tearing protective suits.
Hens produce strong, convulsive wing-flapping after cervical dislocation.
Birds which are killed in rapid succession by this method are difficult to contain due to the violence of these convulsions and raise a lot of dust, spreading the AI virus.
Page 2 of the following article has some interesting information about the strains.
http://www.aphis.usda.gov/stakeholders/downloads/2015/sa_hpai_arkansas.pdf