Recently, I heard of three tourists from Germany drowning in a lake in Alaska. Their boat overturned and they ended up in the water. All three of them were wearing life jackets. This is what I don't understand, how can people still drown if they are wearing a life jacket?
Life jackets do not make one drownproof, just increase your odds significantly.
Our data also show that over 80% of drowning victims were NOT wearing life jackets when found. We know from other data that most of those victims could have been saved had they been wearing a life jacket before the mishap occurred.
But, you ask, what happened to the other 20%, the ones who were wearing life jackets, but drowned anyway?
Those are the primary reasons boaters wearing life jackets sometimes drown. Either the boater is unable to free him- or herself from some type of entrapment, is unconscious or otherwise unable to keep his/her face out of the water, or eventually drowns from numerous mouth immersions over a prolonged period of time.
Of course you are way better off wearing a life jacket but it won't prevent you from drowning in all cases. The other killer if you fall off a boat in the ocean is hypothermia.
In the specific case you mention, both the NY Post and Deutsche Welle say that the cause of death is still being investigated, and both of them point out the low water temperature (the victims were kayaking in a glacier lake). DW mentions that they were not wearing any protection against cold water. At the time of writing, hypothermia seems more likely than drowning -- especially in the case of the victim who was found on top of an ice floe rather than in the water. The NY Post article mentions a water temperature of 9°C, corresponding to an expected survival time of 1-3 hours for the two victims found in the water. Considering that the deceased were all in their sixties, the lower end of this range seems more probable in this case.
It's also possible that hypothermia first led to exhaustion and/or loss of consciousness (probably within 30-60 minutes in those temperatures), which could well put the victims in one of the categories mentioned in Charlie Brumbaugh's answer: ‘unconscious or otherwise unable to keep his/her face out of the water’. Kayakers commonly use type III PFDs, which are often not designed to keep an unconscious person face-up.
PFDs come in various flavours:
The best ones have sufficient floatation around the neck, and enough more flotation on the front compared to the back, than an unconscious victim is naturally rotated onto his back with is face out of the water. The classic design is the "Key hole" design. This is what you find in the lockers on ferries and passsenger ships. I used these for years on canoe trips. The shoulder yoke interferes with a proper paddling stroke. OTOH they are very nice between you and a gunwale when portaging a heavy freighter canoe. You get an interesting tan pattern from them.
The 2nd tier are essentially a vest with foam strips instead of dacron quilting. Cheap ones are a simple zip up and a waist strap. Better ones have straps on the sides to resize the vest to fit snugly, making it more difficult to lose, as well as warmer in the water.
They will float you upright, but if you are unconscious, your face may fall into the water. Does make body recovery easier however. If worn properly (snug) they tend to be about as warm as quilted flannel shirt -- not a win on a hot day.
We required our students to wear a life jacket at all times in the canoes, with the zipper engaged. We were lenient about the waist straps, and having it zipped all way up. However we tried to find a good jumping rock and have them jump into the water with the PFD done up in various bad ways. Some were surprised at how easily it could come off, and how hard it was to put one on in the water.
For reasons of fashion, at one point you could get these in forest green, and a medium blue, instead of the usual international orange, neon yellow, fire engine red. I My current one of these is orange with blue trip, with pockets. I love the pockets on a canoe trip. Snacks, GPS, compass, current map.
Third tier are flotation belts which may or may not keep you upright but reduce vulnerability to undertows. Water skiers seem to like these.
With the first type of life jacket you have to work at drowning in it. It happens. An unconscious victim in choppy water can drown from repeated splashes in the face. This was the cause of death at the Temiskaming incident. (Hypothermia induced drowning)
We used to be able to get the heavy duty foam core ones when they were replaced. (Regulations called for periodic replacements, but most had never been used.) They went to a much cheaper one that didn't withstand the type of abuse they get on canoe trips. (Boat fenders, seats, sleeping pads, portage shoulder cushions) We had to go to the vest type.
Most boaters are using 2nd type. They are more comfortable to wear casually. If not worn properly, or if too large, it is easy to fall through them. Regulators figured that a great lifejacket that isn't worn is not a win.
There are specialist life jackets that amount to a mix of a wet suit top with added flotation along with a 'diaper flap' that can be fastened between the legs. Since these block water circulation beside the chest and in the groin area, the survival time in cold water is greatly increased. They are hot to wear, but generally if you are working with water temps where need this, air temps aren't cooking. Because they have sleeves, even partially unzipped they are unlikely to come off in the water.
In Alaska, I'm betting that hypothermia is part of the picture too. In cold water it quickly becomes impossible to take effective action to save yourself, and soon after mental ability deteriorates.
Something not widely understood yet of critical importance is the cold water shock phenomenon.
Cold-water shock is the first stage of the sudden and unexpected immersion in water which temperature is of 15 °C or lower and occurs during the first minute of exposure. Cold-water shock likely causes more deaths than hypothermia.
The reactions of the body may be muscle spasms and hyperventilation. Other symptoms may be an increase of the pulse and blood pressure. Sudden immersion into cold water may cause cardiac arrest, even for a healthy person. The shock of the cold water can also cause an involuntary gasp reflex that can cause victims to swallow water and drown, even for a good swimmer. Cold water can paralyze the muscles instantly.
A key to survival is to understand this phenomenon, and force yourself to remain calm upon immersion for the first minute.
I've fallen into the water where these people unfortunately died. In almost 40 years I have never been in as much pain as when that happened. The water is sub 45F (~7C) or even colder. Exposure will kill you in minutes from hypothermia.
These people didn't drown, they froze to death.
Two of the tourists’ bodies were found floating in the water, while the third was discovered atop an ice floe, Pierce said.
I was in the water for only 2 minutes and was already in early stage hypothermia when I was pulled out. If not for the quick actions of the people around me, I would have died. That was only 2 minutes, I weigh ~166 pounds (~75 kilograms) and exercise daily so I have a good metabolism and normally can handle wind chills down to 45F but water is a much better conductor of heat than air.
There are a multitude of ways to die in open water while wearing a life vest. It is contingent upon a variety of scenarios whether you survive and the best scenario assumes that the person overboard is in reasonably good health, not intoxicated and doesn't panic. As well, it also assumes that the water is as close to 98.7 degrees as possible, as this is the temp of the average human body, which means you can float longer without dying of hypothermia.
People die in water while wearing a life vest if they are knocked unconscious during the fall and cannot right themselves in the water and thus lose their airway and die. They also die if they are so intoxicated that they simply cannot think straight and end up over exerting themselves or panicking and drowning. The latter is also seen in people with anxiety, who panic upon hitting the water and subsequently become so exhausted that they pass out and die. People also experience shock upon entering a cold body of water and suffer cardiac arrest. That basically it for fairly sudden death in water with a life vest. of course, protracted exposure to the elements, dehydration, hypothermia, starvation and illness are all others if left in long enough.
Without witnessing or knowing anything about what really happened, it is a 100% safe bet to claim that these three people didn't drown. They certainly, without any doubt, died from hypothermia (in particular the one whose body was not found in the water but on an ice floe).
That being said, a life vest makes it easier to keep your head above the surface, but it is by no means a guarantee. Also, note that you can drown with out being submerged, and with very little water being involved at all. This is known as dry drowning. Recently, some smart alecs have coined new fancy terms for the same thing, but it's what it has been called since pretty much forever.
Generally, there exists a multitude of ways you can "drown". One of them is your lungs filling with water, which is surprisingly hard to achieve! That almost never happens (when it does, or appears so, chances are it happened after death).
One way of drowning is just not getting enough air/oxygen into your body despite there actually being rather small amounts of water in your lungs. Another one is not drowning at all, but succumbing to the effect of water, which just happens not to have the right osmolarity, interfering with your blood. Living organisms don't react very positively towards their body fluids being substantially changed within short time. Your heart in particular doesn't like surprise changes in electrolyte concentrations at all. Lung surface is huge, so there's a lot of potential for things going a bad route when you inhale "not just right" fluids. Funnily, it can even happen that people drop dead even hours after being rescued and "safe", for a variety of reasons, not all of which are understood.
Another way of "drowning" is laryngospasm ("dry drowning") which prevents you from breating and which may require only a few drops of water in the extreme case. Or, simply, vagus stimulation which can cause a cardiac arrest in the most extreme case (even if technically, your heart is still doing some escape beating, this is enough to disable you so much that you can no longer withstand the surrounding conditions anyway, which makes it a "permanent condition" very quickly). On particularly sensible individuals, water doesn't even need to go down the throat, the external ear canal will be enough to trigger it.