Safety Considerations for the Design of Modern Elevator Systems

The primary purpose of this work is to conduct an analysis of elevator safety considerations in the United States. This report introduces the development of elevators through its history, definitions and concepts commonly used in the elevator industry.

INTRODUCTION

History and Design Development of Elevators

A traction hoist transfers the lifting power to the hoist ropes through friction between the grooves in the machine drive shaft and hoist ropes. The ropes are ensured to sit in the groove due to the weight of the motor and counterweight.

Classification of Elevators

Electric Elevators
Hydraulic Elevators
Pneumatic Elevator

These building codes are slowly being updated to allow machine roomless traction elevators with a bridging space. Unlike traction elevators, the machine room is located on the lowest floor next to the elevator shaft.

Figure 4: Gearless Traction Elevator [4]

Frequently used electric elevator parts

The factor of safety when choosing suspension ropes can be calculated based on rated load, mass of the car and the counterweight, height of travel, rated speed, rope factor and whether compensating cables are used or not [1]. In technical terms, it refers to the overall framework that consists of the crank, metal framework that is connected to the. The pinion gear, guide rails, safety equipment, car door and door operator are also attached to the car.

The space is usually enclosed and consists of the car, counterweight, guide rails, buffers, landing doors, etc. In addition to the speed limiter, the safety device also functions when the speed of the elevator car exceeds the rated value. Buffers are placed at the bottom of the elevator shaft, beyond the lowest point where the car and counterweight would normally have to travel, to accumulate or dissipate kinetics.

This part of the elevator controls the opening and closing of the door when the destination floors are reached.

Figure 10: A typical passenger elevator (Picture courtesy of Otis Elevator)[1]

ENGINEERING AN ELEVATOR

Technical Parameters

Most of these parameters are given by the manufacturer based on customer needs, building conditions and requirements, and the elevator design. Only with these parameters considered along with safety codes and regulations are elevators designed, manufactured and installed. Due to the varied nature and different needs of elevators for each different building, most elevators except for standard government buildings and transits are made to order.

So each lift is designed independently, and various components are manufactured separately and then installed on site. While every part of the elevator plays an important role, the most critical components in engineering a safe elevator are its brakes, safety gears, suspension cables, buffers, and door operators.

Brakes

I = moment of inertia of all moving parts of the system connected to the high-speed shaft 𝞊 = angular lag of the high-speed shaft. I1 = moment of inertia of rotor, brake drum and worm I2 = moment of inertia of worm wheel and pulley. When selecting a brake, an analysis of the thermal performance of the brake and drum together with the braking torque acting on the drum may be necessary.

The heat generated between the drum and the brake shoes per hour due to friction can be given by, Several repetitions of the test are performed to ensure that the brake produces the desired braking torque. The selection and testing of the brake system are probably the most important steps during an elevator design, requiring careful consideration and consideration of safety regulations for the particular site.

If the vehicle does not move after the drive command has been issued, the brake must be applied to allow the cause to be examined.

Figure 11: A typical DC brake's CAD geometry [13]

Safety Gear

If the rated speed is less than 0.76 m/s, the safety device does not need to have a flexible medium to limit the pressure on the guide rails. If the rated speed is up to 2.5 m/s, safety devices can be of instantaneous type with buffered effect. For rated speeds higher than 2.5 m/s or duplex safety gears, progressive safety gears that limit the deceleration force must be installed.

The overspeed switch is mounted on the overspeed governor and initiates the operation of the safety gears. Safety gears can be designed in several different ways, but all involve catching and holding the elevator car in place when the governor detects overspeed. When the flywheels on the overspeed governor are engaged, this action pulls the levers on the safety gears (Figure 14) attached to the elevator car, which are designed to catch on the guide rails with sufficient deceleration to stop cabin during an emergency, but not much. suddenly the passengers inside may be injured [1].

Ltd., Elevator Progressive Safety Gear OX- 188A, [Online] Available: http://www.kisa-global.com/elevator-safety-devices/elevator- safe-gear/elevator-progressive-safety-gear-ox - 188a.html, Accessed on February 17, 2019.

Figure 12: Overspeed Governor System Arrangement [1]

SAFETY

Elevator Related Accidents in the Past

The six sample accident reports show six different but common types of elevator-related accidents. There are only two other notable incidents involving the free fall of elevator cars due to the breaking of suspension cables in modern rope elevators, and both occurred in 1945. to poor visibility in fog and the lift and safety cables of two lifts broken.

Most elevator-related deaths involve workers working on or near an elevator, and the most common cause is death from falls in the hoistway. Other common causes of elevator-related accidents involve being caught in or between moving bodies, being struck by an object such as the counterweight, collapse, etc. The following Table 2 and Figures 15-17 summarize the available data on worker and passenger fatalities due to elevator-related incidents, and although some of this data may be out of date, it still gives an idea of the most common types and causes.

It can be concluded from the trend seen in Figure 15 - 17 that the most common cause of death in elevator-related incidents is falls, followed by entrapment in or between the elevator and the shaft.

Table 1: Case Study of Elevator Related Accidents in the Past

Elevator Maintenance

Case Study of Elevator Maintenance and Safety Practices at MARTA

If the previous section on elevator related accidents is properly investigated, it can be seen that most of them could have been avoided with proper maintenance and inspection. Therefore, the importance of proper elevator maintenance and inspection protocols and practices cannot be overlooked. MARTA was randomly selected from one of the major transportation systems to understand the current status of maintenance and safety practices.

Unlike most other transit systems in the country, all of MARTA's maintenance is outsourced. MARTA believes that the leading cause of elevator failure is the age of the equipment, which results in increased maintenance and breakdowns. However, technicians must be trained by the contractor to maintain their state license in Georgia.

MARTA requires its contractor to have scheduled preventive maintenance at specified intervals and distinguishes between scheduled versus unscheduled maintenance (unexpected repairs).

Recommended Safety Practices

Proper written safety procedures and trained personnel should be implemented to enforce the required lockout/tagout system. Affected parties should be made aware of all relevant safety codes and legal requirements. Assessments should be carried out with all relevant considerations to ensure energy savings, proper budgeting (do more with reduced budgets), minimize unexpected damage and repairs and extend equipment life.

For example, the rated load of an elevator should only be selected after making an educated assessment of passenger traffic. Technicians should always be available on call if quick repairs are required. A proper data management system should be used to track availability in buildings or agencies that control a large number of elevators.

There must be a properly functioning system in place to ensure that any trapped passenger can always contact emergency services quickly.

THE FUTURE OF ELEVATORS

The ropeless elevator concept, which uses magnetic levitation, is often considered the future of transportation in tall, high-traffic skyscrapers. ThyssenKrupp claims that by using multiple cars in a single axle, waiting times can be reduced to only about 15 to 30 seconds in high-rise buildings [2]. Even the escalators currently in use in high-rise buildings have a height limit before the sheer weight of the cables makes it cumbersome.

When the two elevators were released in 2003 by ThyssenKrupp, it did not see a market in the United States until 2016, when Georgia Tech placed an order after the new safety codes for the integration of two cars in a single axle were approved. Currently, many safety codes require that the drive system be present in a separate location that can be accessed without entering the elevator shaft [1]. Since MULTI and similar linear induction motor technologies integrate a direct drive into the hoist gap itself using magnetic levitation through linear motors, it cannot be commercialized in several states until safety codes are updated or the technology is changed in some.

In fact, several locations that have not adopted the latest ASME safety codes require elevators to be hydraulic only or traction only.

Figure 18: Schematic illustration of cable-free MULTI elevator system [2]

LIST OF REFERENCES

11] Pneumatic Vacuum Elevators, LLC., Principles and Components, [Online], Available: https://www.vacuumelevators.com/principles-components/, Accessed February 17, 2019. Stribling, Bisnow National, Cable Snaps, Elevator Plunges , Residents trapped in Chicago's former Hancock Center, [Online], 19 Nov. 2018, Available: https://www.bisnow.com/national/news/property-. Was a Houston doctor beheaded by a malfunctioning elevator?, [Online], 14 September 2003, Available: https://www.snopes.com/fact-check/houston-elevator-death/, Accessed: 31 March 2019.

Ltd., Elevator Progressive Safety Gear OX-188A, [online] Available: http://www.kisa-global.com/elevator-safety-. Scott, An Elevator That Fact Goes Sideways, Youtube, June 26, 2017, [Online], Available: https://www.youtube.com/watch?v=kdTsbFS4xmI, Accessed: March 17, 2019. Harris, How Stuff Works, How Elevators Work, [online], February 12, 2002, available: https://science.howstuffworks.com/transport/engines-.

Woodford, Explain That Stuff, Elevators, [Online], 15 April 2018, Available: https://www.explainthatstuff.com/how-elevators-work.html, Accessed: 17 March 2019.