To answer your question simply ... no. But depending on the dive profile you may still be ongassing slow half-life tissues during your deep stop..
At the OW level I like to use an analogy. Imagine two sinks connected by a common wall, and with a hole near the bottom of that wall that allows water to flow between them. One sink is your lungs, the other your body. As you descend, it's like pouring water into the first sink ... the hole in the bottom of the common wall lets some water into the other sink which will continue to flow in until the two sinks equalize. That's ongassing. As you ascend, you take water out of the "lung" sink. When it reaches a point where the water in that sink is less than in the "body" sink, water will start to flow the other way. That's offgassing.
Now let's take that analogy a bit further. Since your body comprises lots of different types of tissues that ongas and offgas at different rates, let's imagine that there are a bunch of sinks connected to that "lung" sink and that they all have different size holes ... the slower the tissue ongasses/offgasses, the smaller the hole. As we descend, adding water to the lung sink, the rate at which water flows into those other sinks varies depending on the size of the hole. So as the dive proceeds, the level of water in those sinks will vary, with those connected to the smallest holes (the slow tissues) holding the least water while those with the largest holes (the fast tissues) holding the most. As we begin our ascent, and the water level in the "lung" sink gets reduced, those with the highest levels (the fast tissues) will begin to offgas first. And because they have the biggest hole, they will also offgas the quickest. The slow tissue sinks will still be at a fairly low level, and many will continue having water flowing into them because even though the "lung" sink is being lowered, it's still at a higher level than they are.
This is a simplified analogy, but easy to picture ... and a relatively good analogy of what happens inside your body as the dynamics of the dive change.
As we ascend, we want to manage the rate of change between the "tissue" sinks and the "lung" sink, to help our lungs better remove the excess gas. And one thing we can understand about those sinks is that the closer to equal levels they get, the slower the rate of water flow between them will become. Therefore, the deep stop is really to help our fastest tissues "catch up" by managing the level difference between their sink and the "lung" sink. In other words, the deep stop is for the benefit of our fastest tissues. The trade-off (there are always trade-offs) is that our slowest tissues may therefore continue ongassing while we're stopped. It's for this reason that a deep stop is relatively short ... so that we give the maximum benefit to the fast tissues while at the same time making a minimum payment to the slower ones that are still ongassing. The safety stop is more for the benefit of the slower tissues, because by then the "lung" sink has a relatively low level in it, and all of the other sinks are at a higher level and therefore are flowing back into it.
Using this analogy isn't physiologically accurate, in that there's lots going on that it doesn't talk about ... but it helps to conceptualize ongassing and offgassing for people who have never really thought about it before ... and does so in a way that skips all the math. It also puts into context why a safety stop is recommended ...
... Bob (Grateful Diver)
