There is a theory circulating in the alternate media that the Syrian government did not attack civilians with sarin gas, which would not have served their interests either militarily or politically. The government has nearly won the war already and is probably intelligent enough to realize that using chemical weapons would be an excuse for Western intervention.
The chemical involved was not sarin, the theory goes. And, indeed, the medical and rescue workers are unprotected as they handle the victims and search the site of the disaster. That would lead to death or serious sickness with a skin absorbable toxin like sarin.
So the chemical agent was probably something like phosgene or mustard gas, which the rebels have used in the past and which they are known to manufacture.
So, most likely the Syrian air strike hit a rebel chemical weapons factory or storage facility.
Meaning that the American strike is based on a misunderstanding of the situation coupled with a reluctance to see the war ended with a government victory.