Downunder like elsewhere we have had several biosecurity situations ie farm diseases like horse flu, pig flu, bird flu, well not quite bird flu but many poultery sheds are infected with some virus etc.
Hazmat placarding is quite good however biosecurity situations usually are signed "do not enter biosecurity" with no other details. I can understand the reluctance to disclose publicly what the problem is as it could cause panic.
A mobile phone number should be required to be displayed. Any incoming emergency vehicle could then contact prior to entering the property and ensuring all wash down precautions are undertaken on entering or leaving the site and all quarantine protocols are complied with.
What happens in the States with this type of issue?