Question

A safety-critical software system for managing roller coasters controls two main components: \- The lock and release of the roller coaster harness which is supposed to keep riders in place as the coaster performs sharp and sudden moves. The roller coaster could not move with any unlocked harnesses. \- The minimum and maximum speeds of the roller coaster as it moves along the various segments of the ride to prevent derailing, given the number of people riding the roller coaster. Identify three hazards that may arise in this system. For each hazard, suggest a defensive requirement that will reduce the probability that these hazards will result in an accident. Explain why your suggested defense is likely to reduce the risk associated with the hazard.

Short answer

Three hazards include harness lock failure, exceeding maximum speeds, and insufficient speeds. Defensive measures include multi-sensor validation for harness locks, automated speed control, and minimum speed alerts.

Step-by-step solution

Analyze Harness Lock and Release Hazards

One hazard is the failure of the locking mechanism of the harness. This can result in riders not being securely fastened during the ride. To mitigate this hazard, a defensive requirement could be implementing a multi-sensor verification system that checks the harness lock status before the ride begins. This would reduce the risk because relying on multiple sensors ensures that a single sensor failure doesn't compromise safety, and the ride does not start until all harnesses are confirmed locked.

Assess Over-Speed Hazards

Another hazard is the roller coaster exceeding maximum safe speeds, especially around curves. An appropriate defensive requirement would be to install a speed monitoring and control system that automatically applies brakes if the speed exceeds a certain threshold. This defense reduces risk by preventing the coaster from operating at speeds that could cause loss of control or derailment, thereby ensuring the ride stays within safe operating conditions.

Evaluate Under-Speed Hazards

A hazard may also arise from the roller coaster moving too slowly, which could stall the ride mid-course, especially on upward slopes. A defensive requirement here could be to enforce a minimum speed monitoring system that alerts operators when speeds drop below safe thresholds. This system reduces risk by enabling timely corrective actions, such as increasing the propulsion force to maintain momentum.

Key concepts

Hazard Analysis

Hazard Analysis is a critical step in designing safety-critical software systems for roller coasters. It involves identifying potential hazards or dangers that can arise within the system. In the case of our roller coaster, potential hazards include a failure of the harness locking system, excessive speeds, and insufficient speeds.

Identifying these hazards allows developers to anticipate issues that could lead to accidents. By thoroughly analyzing such possibilities, you can create solutions that prevent these problems from occurring. This proactive approach helps in maintaining the safety of the roller coaster riders throughout their experience. Understanding potential hazards also supports the development of more advanced safety features for future systems.

Defensive Requirements

Defensive Requirements are vital in the context of ensuring safety in roller coaster operations. They are precautionary measures put in place to mitigate or eliminate identified hazards. In the case of the roller coaster's harness, a defensive requirement could be to integrate a multi-sensor verification system.

This means using multiple sensors to verify the locked status of every harness before the ride is allowed to start. Such a system ensures that even if one sensor fails, others will confirm the safety status, reducing the chances of the roller coaster starting with an unlocked harness. Defensive requirements thus ensure a higher degree of reliability and safety by adding layers of security.

Risk Reduction

Risk Reduction is achieved by implementing systems and protocols that minimize the chances of hazards resulting in accidents. For instance, managing the risks associated with speeding involves installing a speed monitoring system that automatically controls or limits the roller coaster's speed.

By having precise control over speed, the risk of derailing or losing control, especially during sharp curves, is significantly lowered. Risk reduction strategies like these are fundamental to ensure that the roller coaster operates within safe parameters, thereby protecting riders and maintaining smooth operation.

Speed Monitoring

Speed Monitoring is an essential component for maintaining the safe operation of roller coasters. It involves using technology to consistently and accurately track the speed of the roller coaster as it traverses the ride.

By monitoring the speed in real-time, any deviation from the safe speed range can be immediately addressed. For example, if the roller coaster approaches a curve too quickly, automatic systems could apply brakes to slow it down to a safer speed. Similarly, if it is moving too slowly and risks stalling, prompts can alert operators to take corrective actions. Therefore, speed monitoring ensures the ride remains within safe speed limits at all times.

Sensor Verification

Sensor Verification is a critical requirement for roller coaster safety, especially regarding harness locks. This involves using multiple sensors to confirm the status of the harnesses — whether they are securely locked or not.

Multi-sensor verification balances the risk of a single sensor malfunctioning by requiring all sensors to agree on the status before allowing the ride to proceed. This redundancy is crucial in safety-critical environments. If one sensor fails, others can still ensure that all harnesses are safely locked, preventing potential accidents due to human error or technical failures. This type of verification is a robust defense against mechanical failures, ensuring rider safety.