What is Safety (Functional Safety)?
Safety, or functional safety, refers to the ability of a system to operate safely in the event of malfunctions, faults, or external influences, so that harm to people, machines, or the environment is prevented. In industrial automation, safety is an essential design principle that is often based on standards such as ISO 13849-1 and IEC 61511.
In OT environments, safety not only protects personnel but also production continuity and corporate reputation.
🧠 What does Safety encompass?
| Aspect | Examples |
|---|---|
| Safety functions | Emergency stop, light curtains, speed monitoring |
| Safe components | Safety PLC, safety relays, certified sensors |
| Risk assessment | RI&E, HAZOP, LOPA, FMEA |
| Redundancy & fault detection | Dual circuits, monitoring for wire break or short circuit |
| Functional design | Safe behaviour during power loss, overpressure, or overtemperature |
| Maintenance & validation | FAT, SAT, test procedures, interval testing |
🔐 Safety vs Security
| Safety | Security |
|---|---|
| Protection against unintentional hazards | Protection against deliberate attacks |
| Focuses on errors, failures, and accidents | Focuses on data leaks, sabotage, and espionage |
| Standards such as ISO 13849, IEC 62061 | Standards such as IEC 62443, ISO 27001 |
| Evaluation: SIL, PL, PFHd | Evaluation: risk assessment, SL |
Well-designed systems take both into account: a vulnerable system may seem safe, yet become hazardous through an attack.
🔧 Important standards
| Standard | Description |
|---|---|
| ISO 12100 | Foundations for risk assessment and risk reduction |
| ISO 13849-1 | Safety-related control systems with PL (Performance Level) |
| IEC 61508 | General standard for functional safety (basis for SIL) |
| IEC 61511 | Functional safety in the process industry |
| IEC 62061 | Safety of machinery control (SIL for machines) |
| ISO 14119 | Interlock systems and locking |
| IEC 60204-1 | Electrical safety of machinery |
| IEC 61439 | Safety of low-voltage switchgear |
⚙️ Components for functional safety
- Safety PLC – Logic for safety functions
- Safety relays – Hardware-based interruption of emergency circuits
- Emergency stop – Direct machine deactivation in case of danger
- Interlock – Restricts access or actions based on machine position
- Safety light curtains and mats
- Encoders/sensors with fault detection
- Redundant power supplies and communication (e.g. PROFIsafe, CIP Safety)
✅ Best practices
| Action | Why? |
|---|---|
| Risk assessment in advance | Identify potential hazards and determine necessary protective measures |
| Use certified components | Ensure conformity and reliability |
| Periodic validation & testing | Confirm that systems still function correctly |
| Training and awareness | Operators recognise hazards and respond correctly |
| Couple safety with Security | Prevent digital attacks from causing physical damage |
📌 In summary
Safety is not a stand-alone system, but an integral part of design, maintenance, and behaviour in OT. Functional safety protects people, processes, and production from the consequences of errors and failures.