Fail-Closed Safety Gates
Architectural patterns for preventing catastrophic failures in veterinary systems.
The Need for Fail-Closed Systems
In veterinary practice management systems, certain failures can have catastrophic consequences. A fail-closed approach ensures that when systems cannot verify safety or correctness, they default to a safe state rather than risking patient harm or data loss.
This white paper explores the architecture, implementation, and operational aspects of fail-closed safety gates in veterinary software systems.
For patient safety errors
Before critical actions
Of all safety systems
Core Safety Principles
Fail-closed systems are built on fundamental principles that prioritize safety over convenience, ensuring that system failures never compromise patient wellbeing or data integrity.
1. Safety Over Availability
When safety cannot be guaranteed, the system must become unavailable. It is better to halt operations than to proceed with uncertain safety.
2. Explicit Verification
All critical operations require explicit verification of preconditions. Implicit assumptions or cached validations are insufficient for safety-critical actions.
3. Graceful Degradation
When non-critical features fail, the system must continue to provide essential safety functions with clear communication about limitations.
Safety Gate Patterns
These patterns provide specific implementations of fail-closed principles for common veterinary software scenarios.
| Gate Type | Trigger Conditions | Fail-Closed Action | Recovery Process |
|---|---|---|---|
| Medication Safety | Dose verification failures, allergy conflicts | Block prescription, require pharmacist review | Manual override with dual authorization |
| Controlled Substances | Inventory mismatches, invalid DEA numbers | Prevent dispensing, notify compliance officer | Physical inventory reconciliation |
| Surgical Planning | Missing pre-op data, consent issues | Halt scheduling, require complete checklist | Complete all required documentation |
| Data Integrity | Checksum failures, audit gaps | Read-only mode, initiate investigation | Restore from verified backup |
Implementation Architecture
Implementing fail-closed safety gates requires careful architectural design that ensures safety checks cannot be bypassed or circumvented, even during system failures.
Key Components
- ✓Immutable safety rule engine
- ✓Real-time monitoring and alerting
- ✓Circuit breaker pattern for integrations
- ✓Audit trail for all safety decisions
- ✓Emergency override procedures
⚡ Critical Design
Safety gates must be implemented at the infrastructure level, not as application features. They cannot be disabled by configuration changes or user permissions.
Testing Safety Gates
Safety gates require rigorous testing beyond typical software QA. They must be proven to function correctly under all failure conditions and edge cases.
Chaos Testing
Intentionally induce failures to verify safety gates trigger correctly. Test network partitions, database failures, and service dependencies.
Scenario Testing
Simulate real-world clinical scenarios including emergencies, high-volume periods, and unusual cases to ensure gates don't impede legitimate care.
Penetration Testing
Attempt to bypass or disable safety gates through unauthorized means. Verify that all attempts are blocked and logged.
Prioritizing Safety in System Design
Fail-closed safety gates represent a fundamental shift from availability-first to safety-first system design. By implementing these patterns, veterinary software vendors can ensure their systems protect patients and practices even when things go wrong.