The p10 and the p30 use the same chart and the same disclaimer, that the manufacturer might produce something different to what the chart depicts, yet the difference between them with the machine off is profound.
The P30 has a vent at the junction on top of the head and another at the nose but both vents are very restrictive and it uses soft hoses which collapse and seal shut if the machine is off and you suck too hard on them, rendering the top vent inaccessible and blocking any additional air that might otherwise be accessible through the machine itself.
I have 3 CPAP machines here and they have all shut down from time to time so from my perspective this is a real issue.
I have 3 different nasal masks and the only one that I considered safe over a protracted period with a dead machine was the Fischer and Paykel Nuance and that was probably, in part, because it leaked so readily and was easily removed.
There must be a way to reduce the risk of these masks when the machine fails. Non-collapsible hoses and an additional one-way valve would be a lot safer than what I am currently using. These kinds of valves are often noisy but if it only operated when the CPAP failed being noisy might be a good thing.
Even if it was at the machine, if it was generous enough, the larger volume of air would reduce the proportion of rebreathed air.
Another option might be to improve the natural airflow potential of the machine itself. Enlarging the filter, fan, and internal airways so that more air can be sucked through the machine after it shuts down.
A more drastic option would be to split the main hose and create a cycle of air from the machine with a one-way inlet valve on the outgoing airflow and an outlet valve on the return flow which terminates at, or through, the machine. This would remove all vents from the mask along with most of the noise and would significantly reduce rebreathing at the mask and facilitate adaptation to an isolated airflow system.
Someone must have considered these and a thousand other options yet they continue to distribute products that are not safe.