For many, spending a day at the beach can involve finding creative ways to enjoy the sand and sea. Building sand castles could be one, and digging holes another, but despite an innocent attempt at some light entertainment, most beach goers might not realise that digging a hole deep into the sand is a hazard that can cost lives.
Between 1997 and 2007 in the United States, collapsing sand holes was the cause of 31 deaths and a further 27 serious casualties, many of whom were children. It can happen when people fall, jump, dig or tunnel in the holes. In most of these cases, the craters were around 2 to 15 feet (0.6 – 4.6 metres) wide in diameter and 2 to 12 feet (0.6 – 3.7 metres) in depth. Some research has found that more people have died from collapsing sand than shark attacks.
It’s important to look at the science behind sand’s attributes to understand how this common component of the seaside experience is much more deadly than you would expect. Depending on the type of beach, sand is made up of differing chemical compounds. The most common quartz sand is a combination of silicon dioxide, whereas tropical beaches are home to coral sand, made from calcium carbonate. The weight of sand is dependent on the materials in question, for example, the more typical brown or beige coloured sand, made up of a number of minerals weighs up to 130 pounds per cubic foot, (2.1 tonnes per cubic metre) whereas the pure white beaches made from quartz sand, when dry, weighs up to 90 pounds per cubic foot (1.4 tonnes per cubic metre).
The issue is, there’s a significant change in sand’s stability depending on whether it is dry or wet. When sand is wet, it is more stable as the surface tension between the sand grains and water is greater, which holds it together. When sand is dry however, the surface tension disappears, causing it to fall apart. Therefore, if there is a pit of sand dug into the ground that has dried, and a passerby is walking alongside, the extra weight around the outside of the hole will cause the sand to collapse in itself and fill the space.
Due to sand’s instability and significant weight, it can be very difficult to rescue someone trapped in a collapsed sand hole. As the grains will fill all available open space, it is impossible for the individual to breathe, and unless rescued within a few minutes, the person will suffocate to death. Therefore, it is recommended that holes should not be dug any deeper than knee height of the shortest person in the group.
The reality is, even the shallowest of craters can cause injury and so it is advised to fill any sand holes you see on the beach to avoid possible harm. If you encounter someone who has fallen in, put whatever seaside objects you have available, such as surfboards or beach chairs around the hole’s edge and focus on clearing sand from the top of their chest whilst exposing their mouth for breath. Mouth-to-mouth resuscitation can be administered as necessary. Furthermore, ensure there is no crowding around the scene of the collapse as this risks more sand filling from the added weight.
