is required to operate some types of AWP. Most protocols advocate training every operator, whether mandated or not. Most operators adopt a checklist of verifications to be completed before each use. Manufacturers recommend regular maintenance schedules. Work platforms are fitted with safety or guard rails around the platform itself to contain operators and passengers. This is supplemented in most models by a restraining point, designed to secure a safety harness or fall arrester. Some work platforms also have a lip around the floor of the platform itself to avoid tools or supplies being accidentally kicked off the platform. Some protocols require all equipment to be attached to the structure by individual lanyards. When using AWPs in the vicinity of overhead power lines, users may be electrocuted if the lift comes into contact with electrical wiring. Non-conductive materials, such as fiberglass, may be used to reduce this hazard. 'No Go Zones' may be designated near electrical hazards. AWPs often come equipped with a variety of tilt sensors. The most commonly activated sensor is an overweight sensor that will not allow the platform to raise if the maximum operating weight is exceeded. Sensors within the machine detect that weight on the platform is off-balance to such a point as to risk a possible tip-over if the platform is raised further. Another sensor will refuse to extend the platform if the machine is on a significant incline. Some models of AWPs additionally feature counterweights, which extend in order to offset the danger of tipping the machine inherent in extending items like booms or bridges. As with most potentially dangerous mechanical devices, all AWPs are fitted with an emergency stop button which may be activated by a user in the event of a malfunction or danger. Best practice dictates fitting of emergency stop buttons on the platform and at the base as a minimum. Other safety features include automatic self-checking of the AWP's working parts, including a voltmeter that detects if the lift has insufficient power to complete its tasks and preventing operation if supply voltage is insufficient. Some AWPs provide manual lowering levers at the base of the machine, allowing operators to lower the platform to the ground in the event of a power or control failure, or unauthorized use of the machine. Rental equipment AWPs are often bought by equipment rental companies, who then rent them out to construction companies or individuals