In 1953 Edmund Hillary and Tensing Norgay conquered Mount Everest, but over in the scientific world the chemist Dr. Hermann Schnell working for Bayer Labs in Uerdingen Germany, invented a new class of plastic called polycarbonates, and so doing, successfully synthesized Makrolon. Polycarbonates are a particular group of thermoplastic polymers. Polycarbonates received their name because they are polymers having functional groups linked together by carbonate groups (-O-(C=O)-O-) in a long molecular chain. In the last 50 years Makrolon has been used in a plethora of products, including eyeglasses, goggles, helmets, automotive glazing and headlights, sheeting for green houses, water containers, and the ubiquitous CD/DVD.
Polystyrene (Poly(1-phenylethane-1,2-diyl)), abbreviated as PS (recycling symbol “6″), is a polymer made from the aromatic monomer styrene (vinyl benzene ), a liquid hydrocarbon that is commercially manufactured from petroleum by the chemical industry. Polystyrene and its origin can be traced back to 1839 when Eduard Simon, an apothecary (pharmacist), distilled an oily substance from a Turkish sweetgum tree, which he named styrol. About one hundred years passed, and various scientists conducted numerous experiments, before German chemist Hermann Staudinger discovered that heating styrol starts a reaction and produces macromolecules, this substance is now known as polystyrene. BASF began commercial manufacture of polystyrene in 1931, when they were part of the monstrous German conglomerate I.G Farben (BASF, Bayer, Hoechst, Afga, etc.). Post World War II the I.G Farben conglomerate was divided back up into the individual companies, and in 1952 BASF invented expandable polystyrene (EPS), which they called Styropor. An interesting adjunct is that Bayer invented Makrolon (used as the outer shell of the helmet) around the same time period.
The safety standards for helmets include a retention system, and an impact test, the latter is done using a hard headform dropped vertically onto a flat and shaped anvil at specific speeds. The US standard is to keep the g forces registered inside the headform below 300 g.
The major components of a helmet, are the outer shell, the foam liner, the retention system and the padding. The hard shell helps spread the impact over a larger surface (specifically to the liner), accentuates sliding and prevents object penetration. The EPS foam helps prevent or reduce brain injury by managing the energy of an impact through its own compression or destruction, and it does that by converting a small part of the crash energy to heat. Its main duty is to slow the stopping process so that the head slows down during its inertial of the impact (deceleration).
The problem is that our heads are soft and malleable, and the brain itself moves around inside a gelatinous ooze (cerebrospinal fluid), so the testing with a hard headform may not be very appropriate for the human skull? One of the major things a helmet cannot prevent is the occurrence of coup-contrecoup (brain rebound) injuries, which can cause concussions, contusions, DIA’s (diffuse axonal injury) and even epidural hematoma.