In every brazing seminar that I teach, I ask if people are aware of any deaths that have occurred from argon. In almost every class someone raises their hand and has a story to tell. When asked if they know of deaths that have occurred from other industrial gases used in brazing (such as nitrogen, helium or hydrogen), no one ever raises their hand.
Too many people are not aware of how dangerous argon can be and that they can easily be overcome by the argon and collapse onto the floor of that hole or pit. There is no warning because argon has no odor (such as is placed in natural gas for our safety), and there are no warning sensations, no breathing spasms, etc. to warn you that you are in an argon atmosphere. When the brain uses up its oxygen reserves (since no fresh oxygen is being sent to it when you are breathing only pure argon), the brain merely shuts itself down, and the person instantly collapses. This can quickly result in that person's death if he/she is not immediately pulled to safety.
How do we know that there are no advance warning signs to so-called “argon poisoning”? Because many people have been pulled out of such situations, having “blacked out” and collapsed from their argon inhalation. When they awake in a hospital bed (or in the company’s sick-room bed), they are surprised to find themselves there. When asked about any sensations they felt or warning signs (such as dizziness, choking, lack of coherence, etc.), they invariably say that no warning signs occured at all. They were doing their work, and the next thing they knew they were waking up in a bed! They were totally surprised by what had happened!