剛找了一下. 美國的國家地理雜誌有稍微提到. 應該不超過3.5G. 因為超過3.5或4G他應該會死. 下面是解釋.

Depending on the speed, a flat spin would could cause anything from headache, shortness of breath, and vision failure to mental confusion, unconsciousness, and burst eyeballs—when pressures exceeding -4 G's build up in the skull, blood and spinal fluid are forced outward, and their main escape routes are through the ocular cavities.

The flat-spin risk can be mediated with a technology first developed for Kittinger: a stabilization parachute to prevent further increase in rotation, deployed on command, or automatically if -3.5 G's are achieved.