We also recommend you wear durable impact resistant protection for your lower face (teeth). We have had players lose teeth and it's a major change and expense.
ASTM is working on a new goggle standard for airsoft which should be published in 2014 based on the current progress. The committee working on it (Committee F08.27) has a few items to review and some comments that require addressing to complete the development process.
Mike Lukas, technical specialist on the F08.27 committee, recommends the following guidelines: