Wow, I really am shocked that so few have responded to this thread and that very few of us are wearing these masks.
I am with you Lorraine, there is no way all the fumes are vented out no matter how good your vent system is.
I wear a half face mask and use P100 filters that are good for gases and fumes plus particulates. I just can't remember the number. Yes, it's uncomfortable, it gets hot, etc, etc. but I figure if I'm going to mess around with dangerous gases and things floating in the air, I'm going to protect myself in any way I can.
What I find really scary - The person I took my one and only lampworking class with so many years ago, had NO ventilation at all. Another glass shop right here in Georgia that had fusing and lampworking classes had NO ventilation at all either. None. There was another lampworker I was going to take a class with some time ago also had NO ventilation in their shop. I was told they would open windows ! Needless to say I didn't take that class.
Thanks for your posts.