some criticism for its non-impact rated construction and vulnerability to debris. Some impacts (particularly at close range with powerful guns) are capable of cracking or damaging teeth. Dentists have reported broken teeth that require root canal and crowns to repair damage. A face mask (like that used for paintball) is recommended to protect eyes and teeth. Metallic mesh masks and mouth guards have recently seen popular use. There are legal issues in airsoft as well as several rules imposed in a game by game basis. Most indoor airsoft fields only allow up to , and most outdoor fields begin capping near the 410 ft/s (125 m/s) for rifles and 525 ft/s (160 m/s) for long-range guns such as sniper rifles. Most outdoor fields also impose a minimum engagement distance for guns firing over a certain range, normally for squad support weapons and sniper rifles. In order for an airsoft gun to cause any serious injury, it would have to be well over these limits and in close proximity. To even reach such speeds, the gun would have to be highly modified. So it is therefore unlikely to cause permanent or serious damage with any stock airsoft gun. The use of metallic BBs, or any foreign objects, is very dangerous for the user and other people and property in close vicinity, and may damage the airsoft gun as well. However, specially designed and built metallic 6 mm BBs for airsoft guns can be found on the market. These metallic BBs should not be used for airsoft play because they can break through goggles and other safety gear. Plastic BBs can be a mixture of PLA and Plastic causing less damage to persons. Although airsoft guns in the United States are generally sold with a 6 mm (0.24in.) or longer orange tip on the barrel in order to distinguish them from real firearms, this is not in fact required by federal law. There is some controversy on this topic as Title 15 of the Code of Federal Regulations, on foreign commerce and trade, stipulates that "no person shall manufacture, enter into commerce, ship, transport, or receive any toy, look-alike, or imitation firearm" without approved markings; these may include an orange tip, orange barrel plug, brightly colored exterior of the whole toy, or transparent construction (part 272.2, formerly part 1150.2). However, section 272.1 (formerly 1150.1) clearly indicates that these restrictions shall not apply