Hi Laura:
ALL the above comments are excellent, and I will also voice a thought that digging in your dust collector may not be the best idea.
However; I AM ALSO ALLERGIC to Alumilite! So yes, it is possible. Alumilite is a Urethane, and yes, folks can get Urethane Sensitivities.
My solution is workable,
very inconvenient, costs a bit, but has been effective:
http://content.penturners.org/library/tools_and_jigs/casting_box.pdf
Whether you try this system or not, these are MY circumstances:
My Docs are at the Cleveland Clinic.
I have had rashes for 2 1/2 years. They get slightly better, but do not go away. Continued exposure to urethane resins will only make them worse. I have tried many (6+ prescription ointments) creams, several pills, none has been effective. The most recent, and has worked the best has been Cyclosporin, but it is hard on the Kidneys, will push your blood pressure up, and is not a long-term possibility... So I really have no good news for you (and I) for a Urethane sensitivity. (Which is quite rare - Alumilite is a very safe, well researched, well used product. So no issues with Alumilite... It's us!).
I have used my "fume hood" only on specific occasions, and it has gone well. A smoke test does show that all the fumes get expelled outside of my garage, rather than anywhere close to me. I will use it without any concern about worsening my sensitivity.
However... I do have a blessed Back-up supervisor: My Wife! She is a PhD Chemist in Polymer Chemistry (yup, scary knowledge about Urethanes); has tested my fume hood; has tested my air circulation; has tested my fume hood concentrations; and has repeatedly told me: "You have two choices: Eliminate any possibility of further exposure (Rashes will only get worse); or eliminate the hobby (Casting)." NOTE: My wife has placed Assistant Chemists on Medical Disability due to Urethane Sensitivities... They simply cannot be in the lab. (How the heck I married an expert in Urethanes 32 yrs ago and developed a hobby using urethanes is beyond me!).
OK... Laura, there are MANY avenues to enjoy penturning (You know where this is going!). IF, you have a Urethane Sensitivity, I'd seriously recommend you not continue using Alumilite unless you ca be assured of a "No Exposure" environment. Possible? - Yes. Do I do it? - Yes.
I will happily trade PM's with you if that may be helpful!
Finally, I will simply state that as a "hobbist" with penturning - I will willingly (but grudgingly) forgo casting to continue with this pastime!
As many others have cautioned younger woodturners - "Don't go cheap on the dust collection, your lungs will be grateful." I will caution: "Don't work with chemicals that are not suited for you - there are too many other options for penturning."
Most Importantly! Welcome, continue to ask questions, and have FUN!
Best Regards, Mark