I recently received a very good question about this through fet, and I would like to share my thoughts with the community as a whole. There is a lot of concern about limb discoloration in photos and in the dungeon setting from those who are less familiar with rope (and even those who are more so). This is what I typically teach:
I have yet to find a really good study on how long in rope bondage is safe, but we use tourniquets all the time in orthopedic surgery without damage to the limb. The salient principles are as follows. Please keep in mind that health issues vary widely, and generalizations are limited.
Essentially dark or dusky color (purple, red) is not a very big deal as long as sensation and active mobility of the limb are still intact. In theory there may be a risk of blood clot in someone who is medically predisposed, but those usually take a fair amount of time to form inside the veins. I usually use a time limit of 15-30 minutes or loss of sensation or mobility as my guideline to when things need to be off-loaded or untied. Focal sensory loss (ex: just a couple fingers) is usually nerve-related and should be addressed quickly. But diffuse tingling in an entire limb is typically due to vascular congestion.
Rope around a limb acts like a tourniquet of sorts, most commonly allowing blood to pump into the limb through the arteries but preventing blood from exiting the limb through the veins. Pressure builds, and small nerve endings throughout the limb get stimulated. Diffuse tingling is the most common way this presents. Due to the increase in fluid in the limb, it may be harder to move your fingers or toes because of compression of muscles as well. In theory, enough buildup of pressure in a limb could cause also secondary major nerve compression (compartment syndrome). So be sure you (or your partner) can still do finger sensation checks and hand/wrist motor function checks if you are getting diffuse numbness from vascular congestion. If you can’t tell if you have radial nerve issues because your entire arm is numb, then you can’t be as proactive about your own safety (or your partner’s).
Ultimately, when in doubt, I recommend erring on the side of caution. Remove load from the tie that seems to causing the problem by lifting the person in rope with your arms or by lowering them to the ground. Untie or cut rope if needed. Never cut rope that is under load… this can cause more damage.
As congested blood starts to leave the limb, sensation and motor function should quickly return to normal. Expect “pins and needles”. If return of function is slow or incomplete, it is very important to seek medical attention.
Another special note: if you have Raynaud’s or peripheral vascular disease, your timeline for toe and finger bindage is very limited! Do rope in warm environments only.
I hope this helps! Happy roping!