Some of these tools are very dangerous until the point that they never should be allowed. An individual buys one, tries to use it and there's a risk of explosion. If a pressure cooker has only a single valve, the own food inside the cooker may block it creating a bomb inside the kitchen. A good reason to remember that in some scenarios who produces pressure cookers cannot save (you know, about the lucrative viewpoint) in materials or create a poor design without security systems to avoid this kind of lamentable result.
Newly, the need for legislation is a must! It's not the first time that a person dies thanks to a poor design of the pressure cooker. It needs a specific regulation because the danger.
The explosion happens to a percentage of the population, and the severity of it is in dependance of multiple factors like if you are in the kitchen, the quantity of liquid inside the cooker or also the structure or the material. It also necessary to remember that the material must be free of imperfections thus avoiding an eventual breakage, providing extra width for more security in the union area of the two pieces.
A solution: a valve with multiple entrance holes, a filter to the valve (like a cullender, with multiple holes and screwed so the user cleans it after use), a second valve of security and finally a design to impede an explosion if all the other methods fail —almost impossible in mathematical ratios— like a hole somewhere that allows the seal to break or similar.
Today, it's dangerous to use several pressure cookers and sometimes the user doesn't know the risks.