Elevators are critical vertical transportation systems in modern buildings, and their safety performance is governed by stringent international standards and technical regulations. To mitigate potential hazards such as overspeed, free fall, door entrapment, and overload, elevators integrate a comprehensive suite of safety and protective devices—designed to prevent accidents, halt abnormal operations, and ensure passenger security in emergencies. This article systematically elaborates on the core safety mechanisms, auxiliary protective features, escalator-specific safety devices, and high-rise elevator safety systems, aligned with global standards including ASME A17.1/CSA B44, EN 81-20/50, and ISO 22559.

 

Safety devices in elevators are engineered to comply with mandatory international standards, ensuring uniform performance and reliability across regions:

- ASME A17.1/CSA B44: The primary safety code for North America, specifying design, construction, installation, and maintenance requirements for elevators and escalators—including load capacity limits, emergency response protocols, and component durability.

- EN 81-20 (Europe): Governs the safety of new passenger and goods elevators, emphasizing risk assessment, safety functions (e.g., overspeed protection), and accessibility for persons with disabilities.

- EN 81-50 (Europe): Focuses on safety requirements for existing elevators, outlining retrofitting standards for aging systems to meet modern safety criteria.

- ISO 22559: International standard for elevator safety and performance, providing global guidelines for risk reduction, emergency operation, and test methods.

 

These devices form the primary defense against catastrophic failures (e.g., overspeed, free fall) and are mandatory for all elevators:

 

2.1 Overspeed Governor (Overspeed Safety Lock)

- Technical Function: A mechanical speed-monitoring device installed in the elevator machine room, directly linked to the elevator hoistway via a steel rope. It triggers protective actions when the cab exceeds 115% of the rated speed (EN 81-20 requirement).

- Operation Mechanism: When overspeed is detected, the governor activates a mechanical clutch to engage the safety gear (anti-fall device) and cuts off power to the elevator drive system. For high-speed elevators (≥2.5 m/s), electronic speed sensors complement mechanical monitoring for dual protection.

- Standards Compliance: Must undergo annual calibration to ensure speed detection accuracy (±5% tolerance).

 

2.2 Safety Gear (Anti-Fall Safety Device)

- Technical Function: Mounted on the elevator cab frame, it is the final defense against free fall. When activated by the overspeed governor, it clamps onto the guide rails to decelerate and stop the cab within a safe distance (≤1.5 m for rated speeds ≤1 m/s).

- Types: 

  - Wedge-type safety gear: For low-to-medium speed elevators (≤2.5 m/s), using wedge-shaped jaws to grip guide rails.

  - Disc-type safety gear: For high-speed elevators (>2.5 m/s), providing uniform clamping force and stable deceleration (0.2–1.0 g, per ISO 22559).

- Key Requirement: Must be tested every 5 years via load-drop tests to verify clamping performance.

 

2.3 Car Safety Lock (Blocstop)

- Technical Function: A secondary locking mechanism installed on the cab or counterweight, preventing uncontrolled horizontal or vertical movement if the primary suspension system (hoist ropes) fails.

- Operation Mechanism: Engages automatically when rope tension is lost, locking the cab to the guide rails via spring-loaded pawls. Complies with EN 81-20’s "redundant safety" principle, ensuring no single point of failure.

 

These devices enhance day-to-day safety by addressing common hazards such as door entrapment, overload, and emergency communication:

 

3.1 Emergency Stopping System

- Technical Function: Integrates manual and automatic emergency brakes. Manual activation via emergency stop buttons (located in the cab and machine room) cuts power to the drive system and engages the safety gear. Automatic activation occurs during critical faults (e.g., voltage loss, hoistway intrusion).

- Safety Requirement: Buttons must be red, mushroom-shaped, and require a twist-to-release reset to prevent accidental activation.

 

3.2 Door Safety Systems

- Safety Edges and Light Curtains: 

  - Safety edges: Rubberized contact sensors mounted on door panels; trigger door reversal if pressure (≥5 N) is detected (ASME A17.1 standard).

  - Light curtains: Infrared sensor arrays (32–64 beams) forming an invisible barrier across the door opening; detect obstacles as small as 5 mm and reverse doors within 0.5 seconds.

- Door Interlocks: Prevent elevator operation unless cab and hoistway doors are fully closed and locked. Electrical interlocks verify door closure, while mechanical interlocks prevent forced door opening from outside the cab.

 

3.3 Emergency Communication & Alarm Systems

- Intercom System: Hardwired or wireless communication linking the cab to a 24/7 monitoring center or building management. Complies with EN 81-20 requirements for clear audio transmission (signal-to-noise ratio ≥30 dB).

- Emergency Alarm Button: Audible alarm (≥85 dB) and visual indicator (flashing red light) to alert building personnel of emergencies. Modern elevators integrate two-way video communication for remote assistance.

 

3.4 Load Capacity Limiter

- Technical Function: Weight-sensing device (strain gauge or pressure sensor) installed under the cab floor, preventing operation if the load exceeds 110% of the rated capacity (ISO 22559).

- Operation Mechanism: Triggers an audible/visual alarm and locks the elevator doors until excess weight is removed. High-precision models (±2% load accuracy) also prevent uneven loading (e.g., unbalanced weight distribution).

 

While the focus is on elevators, escalators (classified as vertical transportation systems) include specialized safety features:

- Emergency Stop Buttons: Red, easily accessible buttons at the top/bottom landings and intermediate positions; halt the escalator within 2 seconds of activation.

- Skirt Brushes & Guards: Nylon brushes (60–80 mm long) mounted along the skirt panels (between steps and side panels) to prevent clothing or objects from being drawn into the gap (≤4 mm gap width per EN 81-10).

- Handrail Speed Synchronization: Sensors monitor handrail speed (±2% of step speed); trigger an alarm and stop the escalator if the difference exceeds 15% for 3 seconds, preventing passenger falls.

- Step Deflection Sensors: Detect abnormal step movement (e.g., sagging, jamming) and stop the escalator to avoid step collapse.

 

High-rise buildings (≥20 floors) require advanced safety features to address unique hazards (e.g., seismic activity, fire):

- Seismic Safety Systems: 

  - Seismic sensors (accelerometers) detect ground motion exceeding 0.15 g (for moderate seismic zones) and trigger elevator shutdown to the nearest safe floor. Doors open automatically, and passengers are evacuated before hoistway damage occurs.

  - Post-seismic inspection protocols (per ISO 22559) require elevator systems to be tested for structural integrity before reoperation.

- Firefighter’s Emergency Operation (FEO) Mode: 

  - Activated via a dedicated key switch in the lobby, overriding normal operation to allow firefighters to control the elevator. Features include:

    - Direct access to all floors (bypassing floor locks).

    - Enhanced ventilation (pressurization systems to prevent smoke inhalation).

    - Emergency lighting (≥1 lux at floor level) and heat-resistant components (rated for 200°C for 1 hour).

- Hoistway Pressure Relief Valves: Prevent hoistway pressurization during fires or explosions, reducing structural stress on elevator doors and cab.