It turns an unconscious person face-up and keeps their airway clear.

That single capability is the whole distinction.

Buoyancy is concentrated at the chest and behind the head so the wearer rotates.

A buoyancy aid keeps a conscious swimmer afloat and does not turn anyone.

A face-down casualty in calm water drowns as reliably as one with no jacket at all.

Choosing between the two starts with whether the wearer might be unconscious.

Where it is - distribution rather than quantity produces the turning action.

The same total buoyancy spread evenly will float someone and not turn them.

Concentrating it at the chest and behind the head rotates the wearer onto their back.

Buoyancy level still matters for how high the wearer floats and what they can carry.

Higher levels are specified for offshore work and heavy clothing.

Both properties are stated, and both are part of the selection.

Inflatable jackets get worn because they are slim; inherent buoyancy works without any mechanism.

The most common reason for drowning while wearing a life jacket is not wearing it at all.

A slim inflatable worn as a harness removes that objection.

Inherently buoyant jackets need no service beyond inspection and cannot fail to inflate.

They are bulky and hot, which is why they are often left off.

Inflatables depend on a cylinder, firing head and bladder, all needing periodic service.

Automatic, for anyone who might be unconscious in the water - manual requires the wearer to act.

Automatic heads fire on water contact without any input.

Manual heads need a toggle pulled, which an unconscious person cannot do.

Automatic versions also inflate in heavy spray or if stored damp.

That is an inconvenience rather than a reason to choose manual for at-risk work.

Manual heads suit specific situations such as working under deck where inflation would trap someone.

It stops the jacket riding up over the wearer's head when they enter the water.

Without it, buoyancy pushes the jacket up and the wearer down through it.

Jackets are supplied with them and they are routinely left unfastened.

That removes much of the jacket's value in the moment it matters.

It also keeps the jacket positioned so the turning action works as designed.

Checking that straps are fastened is a quick and worthwhile supervision point.

Heavy clothing, tools, boots and equipment all reduce effective buoyancy and can defeat the turning action.

Waterlogged clothing adds substantial weight.

Tool belts and equipment can hold a wearer face-down against the jacket's action.

Required buoyancy level rises with what is being worn and carried.

That is why offshore and heavy-clothing work specifies higher levels.

Selecting on the lightest expected clothing is a common and consequential error.

Periodic inspection and service of the cylinder, firing head and bladder, at intervals set by the manufacturer and the regime.

Cylinders are weighed to confirm they are full and not corroded.

Firing heads have expiry dates and are replaced rather than tested.

Bladders are inflated and left to confirm they hold pressure.

A jacket that has been inflated needs rearming before it will work again.

Records of service are normally required and are what demonstrates the equipment is fit for use.