Hot tubs have been in development for decades. The trend started simply enough with the idea that a water pump can route water to jets that can provide a hydromassage within a contained vessel.
The first hot tubs were made of barrel-like material and came in round wooden shapes. Typically these may have leaked through the wood and bacteria could accumulate since the material was porous.
As hot tubs developed and were refined, the acrylic hot tub came into being. Higher end acrylic such as that made by Lucite or Aristech Acrylics is non-porous and easy to clean. The material can also be formed to any shape desired by the vacuum forming process.
Some safety features included in hot tubs over the years include slip resistant footwell, the requirement that there be at least two different paths for water to take through a suction intake as it is routed to the pump for purposes of avoiding hair entrapment issues, and many more.
Jacuzzi covers come with mandatory safety straps in order to keep the little ones out of the spa and the dangers that a container of water can possess around small children. Covers also have cover locks which can sometimes substitute the need to have a fence around the spa to meet local code requirements.
The spa electronics have also become advanced as more safety features are incorporated in the electronics. Some safety features as implemented by Balboa Instruments, manufacturer of premium hot tub components and electronics, include automatic heater shutoff in the event of inadequte water pressure and automatic freeze protection for the winter.
Hot tubs are being made safer all the time, but other factors for safe hot tub use is to limit alcohol use, have a handrail or safety steps to get into and out of the hot tub, and keep the water chemistry balanced.
Have fun using your hot tub safely!