Hughes500 is quite right
There is far too much worry about Vortex Ring State and not nearly enough about avoiding entering OGE conditions with too little power margin. The number of real VRS accidents is insignificant, but the number of accidents due to "falling through" while trying to enter an OGE hover is very real and happens very often. In fact, many of those accidents are labeled "Vortex Ring State" accidents. Many experts try to differentiate these two by calling the Power limiting problem "Power Settling".
To encounter true VRS you must be descending nearly vertically at somewhere near your downwash velocity (at least 75% of your downwash velocity), which is at least 700 feet per minute in a Robbie and something like 2000 feet per minute in a large helicopter. If you need tips on how to avoid VRS, try this tip:
"Avoid 700 foot per minute near vertical descents".
Here is a plot, where 1.0 on the left axis is about 1000 FPM for a Robinson, 2000 for a 412 and 2500 for an S-76
How to avoid the other power problem? Power Settling occurs when you try to Hover OGE with too little power margin, typically 5% or less extra power above that needed for HOGE. If you try to hover with no margin, any descent will require a bit more power, so any rate of descent will start an inexorable fall. The US Army requires at least 8 to 10% more power than the OGE chart to operate with relative comfort while continuously OGE.