What Are Components Offering Well-Tried Safety?
Introduction to Well-Tried Safety Components
In industrial automation, ensuring the safety of personnel, equipment, and processes is critical. One essential concept under international safety standards like ISO 13849-1 is the use of “well-tried safety components.” These are components that have been proven in use over time, are reliable in safety-critical applications, and offer predictable behavior under fault conditions.
Well-tried components reduce design complexity, enhance reliability, and are often key to compliance with machinery safety directives. This article explores what qualifies as well-tried components, examples, their use cases, and how they contribute to safety integrity.
What Does “Well-Tried Safety Component” Mean?
Definition from ISO 13849-1
According to ISO 13849-1, well-tried safety components are those:
- Used widely in similar applications
- Have proven reliability in safety-relevant environments
- Have documented evidence of performance and failure modes
- Offer low failure rates and predictable diagnostics
These components are generally non-programmable mechanical or electromechanical devices that have undergone extensive field testing.
Characteristics of Well-Tried Components
To be considered “well-tried,” a component must exhibit:
1. Proven in Use
It should have an established track record in safety applications without causing unintended operation or hazard.
2. Predictable Failure Behavior
The component should fail in a known, safe mode—e.g., a normally closed contact failing to open or fuse blowing under overload.
3. Diagnostic Coverage
The design must allow for detection of faults, either manually (through inspection) or automatically (via feedback loop or redundancy).
4. High Availability in Industry
These components are widely used across multiple sectors (e.g., food, oil & gas, automotive) and are supported by multiple manufacturers.
Examples of Well-Tried Safety Components
| Component Type | Description | Application Example |
|---|---|---|
| Safety Relays | Monitor emergency stop, light curtains, or two-hand controls | Emergency stop circuits |
| Limit Switches (mechanical) | Detect physical limit or position | Safety interlock on doors |
| Mechanical Interlock Devices | Prevent access during hazardous operation | Machine access doors |
| Pressure Switches | Monitor pressure within safe limits | Compressors, hydraulic systems |
| Safety Contactors | Isolate power to motors or machines | Motor control safety circuits |
| Fuse Links (rated) | Provide circuit protection with predictable tripping | Power safety cut-off |
| Guard Switches (non-coded) | Detect guard opening | Conveyor belt enclosures |
| Hardwired E-Stop Push Buttons | Manual override for emergency shutdown | Operator panels |
Common Applications in Industry
1. Emergency Stop Systems
In emergency stop systems, well-tried relays and hardwired pushbuttons ensure immediate shutdown. The redundant and mechanical feedback in these circuits enhances fault tolerance.
2. Safety Door Interlocks
Well-tried components like mechanical limit switches or guard switches detect door position, ensuring machinery only runs when access panels are secured.
3. Overload and Pressure Protection
Fuses and pressure switches ensure systems shut down under abnormal conditions—such as overpressure or current surges—minimizing risks of explosion or fire.
4. Two-Hand Safety Controls
Well-tried electromechanical safety relays are used to verify that both hands of the operator are on the buttons before a press or cutting machine engages.
Advantages of Using Well-Tried Safety Components
- ✅ Compliance with ISO/IEC standards
- ✅ Lower design and approval costs
- ✅ High reliability and fault predictability
- ✅ Ease of maintenance and troubleshooting
- ✅ Improved availability from multiple vendors
Difference Between “Well-Tried Components” and “Well-Tried Safety Principles”
It’s essential to differentiate between:
- Well-tried safety components: Physical devices like relays, switches, fuses, etc.
- Well-tried safety principles: Engineering methods such as redundancy, fail-safe logic, or diversity that enhance functional safety.
For instance, using dual-channel safety relays with feedback is a well-tried principle, while the relay itself is the well-tried component.
When Not to Use Well-Tried Components
There are limits to their effectiveness:
- ❌ In complex, programmable systems (e.g., PLC-based logic), reliance on well-tried mechanical devices is not sufficient.
- ❌ In environments with high electromagnetic interference or harsh chemicals, mechanical switches may degrade faster.
- ❌ In advanced SIL 3+ systems, higher diagnostics and fault tolerance beyond what well-tried components offer may be necessary.
Role in Performance Level (PL) and Safety Integrity Level (SIL)
Well-tried components typically contribute to systems achieving Performance Level (PL) c or d under ISO 13849. However, in systems requiring PL e or SIL 3, they must be complemented with:
- Redundancy
- Continuous diagnostics
- Diversity in hardware or software
Best Practices for Integrating Well-Tried Components
1. Use in Series with Feedback
Combine switches with diagnostic feedback and redundant channels to improve reliability.
2. Follow Manufacturer Recommendations
Only use components within their rated electrical and mechanical limits.
3. Document Proven Use
Maintain documentation of where, how long, and how often the component has been used safely.
4. Regular Testing and Maintenance
Conduct periodic inspections and loop checks to validate component functionality.
Conclusion
Well-tried safety components remain an integral part of industrial safety systems, particularly in applications that require simplicity, reliability, and proven effectiveness. When applied correctly, they help facilities meet international standards like ISO 13849-1 and ensure operator protection with minimal complexity. However, they are not a one-size-fits-all solution. Modern systems often require a blend of traditional components and smart diagnostics to meet today’s high safety expectations.
Choosing the right mix of proven components and design principles is the key to building cost-effective and compliant safety systems in any industry.