They calculate the following relative risk rates:
Silent: 0.0012 (1x silent rate)
Speaking: 0.0058 (4.98x silent rate)
Shouting / singing: 0.0350 (29.91x silent rate)
Heavy exercise: 0.0817 (69.83x silent rate)
IMHO, you could may argue for a risk factor of 1⁄10 compared to heavy exercise (which is 7x the silent rate), but my gut is that 1⁄5 (14x the silent rate) would be more likely, and something like 1⁄3 (23x the silent rate) would be a better and more conservative choice
OK, did some digging. The relevant source is table 2 from Peng et. al., Practical Indicators for Risk of Airborne Transmission in Shared Indoor Environments and their Application to COVID-19 Outbreaks.
They calculate the following relative risk rates:
Silent: 0.0012 (1x silent rate)
Speaking: 0.0058 (4.98x silent rate)
Shouting / singing: 0.0350 (29.91x silent rate)
Heavy exercise: 0.0817 (69.83x silent rate)
IMHO, you could may argue for a risk factor of 1⁄10 compared to heavy exercise (which is 7x the silent rate), but my gut is that 1⁄5 (14x the silent rate) would be more likely, and something like 1⁄3 (23x the silent rate) would be a better and more conservative choice