So my Sondors is governed at 20 mph and I typically am moving at 16 to 17. Anything over that and you need a full helmet and leathers.
Assuming a 180lb rider hitting a stationary object
20mph collision = 3600lbs of force
30mph collision = 5400lbs of force
Furthermore a 2020 research study out of China showed a significant fatality risk "The analysis results show that, as for e-bike side collisions and e-bike impact speed is 20 km/h, the fatality risk of riders is approximately 2.9% at vehicle impact speed of 30 km/h, 23% at 50 km/h, 50% at 60 km/h, and 90% at 80 km/h"
23% fatality at 30mph
50% fatality at 37mph
Obviously crash dynamics are not this simplistic but shows the amount of force than can be exerted on a body. Your results may vary and there are tons of variable factors
https://www.tandfonline.com/doi/abs/10.1080/15389588.2020.1747614
https://www.mdt.mt.gov/visionzero/people/buckleup/deadly-equation.aspx