[hennell]

The articles comments on acrilic conversion factors are (obliquely) about that. Essentially for any construction material you have a failure rating and a factor of safety - the allowable load is failure divided by FOS, so your materials working load is usually significantly under its failure load.

Equipment rated for depths of 1,300 will be capable of several times that, possibly only reaching immediate material failure at 8,000 meters. But there's a reason you have a FOS; you want to be well within your material limits, not pushing it close to breaking point. After multiple trips that material could be weaker, or an unexpected stress could cause early failure.

[Animats]

See "When acrylic aquariums fail", in Plastics World.[1] That article lists the major acrylic aquarium failures up to 2018. Since then, the AquaDom, listed in the article, failed.[2] Not the same problem, but does involve thick acrylic sections under water pressure.

Acrylic does not come without drawbacks. The engineer needs to have full knowledge and understanding of these drawbacks to successfully design, manufacture and assemble an aquarium that will stand and support aquatic life for years. To ensure longevity, the typical large aquarium is designed with a factor of safety of 11 to 12. This may seem high, but when one considers the implications if one of these large aquariums were to fail, and the sudden, catastrophic event that occurs when they do fail, it becomes more understandable and acceptable. Unfortunately, aquariums have failed for various reasons, leading to tremendous damage, huge monetary losses and, at times, complete loss of the aquatic life. There have been high-profile public aquarium failures, which typically involve huge aquariums, as well as private aquarium failures that range from several hundred to thousands of gallons of water loss. Some common reasons why acrylic aquariums can fail include:

- Poor bonding of acrylic panels creating a weak seam

- improper installation

- poor manufacturing of the acrylic panels, resulting in inferior strength and stiffness

- residual stress molded or formed into the panel during manufacturing

- introduction of large gouges or notches that can significantly increase stress in the panel

Unfortunately, these issues commonly do not reveal themselves during inspection, assembly or the initial setup stages. Further, when the actual failure event does occur, which is typically months to years after installation, it is quick and catastrophic. The seam or crack opens nearly instantaneously without warning. The phenomenon behind this is called creep rupture—the disentanglement of the molecules of plastic over time, at a stress level significantly below the yield strength—yes, below the yield strength—of the plastic.

[1] https://www.plasticstoday.com/materials/when-acrylic-aquariu...

[2] https://www.newsweek.com/aquarium-explosion-hotel-aquadom-fi...

[ekidd]

According to the article:

> Ramsay grabbed a copy of Stachiw’s acrylic handbook from his spare bedroom. When Stachiw’s team was doing its tests, “they would pressurize it really fast, the acrylic would implode, and then they would assign a conversion factor, to tabulate a safe diving depth,” he explained. “So let’s say the sample imploded at twelve hundred metres. You apply a conversion factor of six, and you get a rating of two hundred metres.” He paused, and spoke slowly, to make sure I understood the gravity of what followed. “It’s specifically not called a safety factor, because the acrylic is not safe to twelve hundred metres,” he said. “I’ve got a massive report on all of this, because we’ve just had to reverse engineer all of Jerry Statchiw’s work to determine when our own acrylic will fail.” The risk zone begins at about twice the depth rating.

So apparently acrylic is not tested or rated in a way that gives you a simple "safety factor." But going by this quote, the acrylic might have hypothetically been tested to implode around 7,800 meters, which means that anything over 2,600 would be in the "risk zone."

A more important lesson is that once you know you're dealing with a narcissist or a liar, you can't "correct" for their lies. You basically need to throw out all the data they provided, and redo any analysis from scratch.