Editing Compressed-air car (section)

===Compressed air tanks and collision safety===
{{Main|Compressed-air energy storage}}

The tanks must be designed to safety standards for a [[pressure vessel]]. [[ISO 11439]] is a similar standard, for compressed natural gas tanks.<ref>{{cite web|url=http://www.iso.org/iso/catalogue_detail?csnumber=33298 |title=Gas cylinders – High pressure cylinders for the on-board storage of natural gas as a fuel for automotive vehicles |publisher=Iso.org |date=2006-07-18 |accessdate=2010-10-13}}</ref>

The air storage tanks usable in compressed air cars can be low pressure (9 atm) or high pressure (240+ atm). Thus, they can be made of [[composite material]]s like [[thermoplastic]]s and fiber reinforced thermoplastics,<ref name="compositesworld.com">{{cite web|url=https://www.compositesworld.com/articles/thermoplastic-composite-pressure-vessels-for-fcvs |title=Thermoplastic composite pressure vessels for FCVs |publisher=compositesworld.com |date=2015-02-01 |accessdate=2015-02-01}}</ref><ref name="plastics.gl">{{cite web|url=https://www.plastics.gl/automotive/high-pressure-gas-tanks-in-thermoplastic-composites/ |title=High pressure gas tanks in thermoplastic composites |publisher=plastics.gl |date=2014-05-01 |accessdate=2014-05-01}}</ref> This might permit low priced tankage. It might be made by [[rotational molding]]. Such tanks can be much lighter than [[Lithium iron phosphate battery|lithium-iron]] batteries and 70% lighter than steel tanks. They resist rust from air, water and condensation. They last longer with less maintenance.

To reduce car weight further the [[pressure vessels]] can be used as structural parts of the [[chassis]]. Advanced 700-atmosphere pressure vessels have been developed for [[hydrogen cars]]. [[Crash tests]] showed good safety. Fiber reinforced [[thermoplastic]] tanks only rupture in collisions. They do not shatter or explode.<ref name="hyundaimotorgroup">{{cite web|url=https://news.hyundaimotorgroup.com/Article/Hydrogen-Tank-Safety-Proven |title=OHydrogen Tank: Safety Proven (OA-ICAES) System  |publisher=hyundaimotorgroup |accessdate=2019-07-13}}</ref>

Hydrogen tanks require ‘high strength’ to prevent rupture and ‘high stiffness’ for durability. Strength resists an external force. Stiffness maintains a shape. Carbon fiber hydrogen fuel tanks are as light as plastic but six times the strength of steel and four times the stiffness. “When a bullet penetrates a hydrogen tank, it does not explode. Instead, hydrogen leaks out through the bullet hole. In a standard collision test, not even a tiny amount of hydrogen was detected because none had leaked out."<ref name="hyundaimotorgroup"/>