If the announcement is seen as price sensitive then a halt can be requested - but usually a 'pre-notice' of 15 minutes is all that is needed. Trading halts are not always good as those wanting to get in/out can be hampered by inability to transact, and a stock that is always being halted will affect those seeking ability to sell and use funds for other stock purchases etc.
This morning the stock was in 'pre notice', which was a 15 minute halt.
ISX Price at posting:
17.0¢ Sentiment: Buy Disclosure: Held