This is true and, tbh, that petition is very thin on information. The argument at the moment is that the current standard of 0.1mg/m3 is too high and that this should be reduced to the level recommended by industrial hygienists of 0.025mg/m3.

There's also a push to require more effective monitoring and enforcement to ensure employers are keeping to these standards.

It's not so much a case of arguing that there are no standards at all but a push to have Safe Work Australia look at ways they can improve the standards beyond what they currently are. There's still far too many people developing lung cancer from occupational exposure to silicosis dust so there's still plenty of room for improvements to be made.

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Quick link to the cancer council fact sheet on the subject: https://www.cancer.org.au/preventing-cancer/workplace-cancer/silica-dust.html

(It's pretty much an ELI5 version of the facts but it's a lot more readable than a lot of the literature on the subject and should hopefully give you an understanding of why silicosis is a serious issue that we should be looking at)