SIL/PF Level Determination

Determining the appropriate Safety Integrity Level (SIL) or Performance Factor (PF) requires a thorough risk assessment. The Safety Evaluation Tool's guidance on "missing arm or death" is a starting point, but needs context.

Risk Assessment for Your Application

Your scenario involves a gas plant with an ATEX Zone 1 classification, a filling process controlled by a PLC, an on/off valve, and a pressure transmitter. The primary risk is a gas leak due to valve failure or pressure transmitter malfunction. This could lead to a flammable atmosphere and potential ignition.

Risk Factors to Consider:

• Gas Toxicity: The specific gas being handled impacts severity.
• Leak Rate: How quickly could a leak develop and reach a dangerous concentration?
• Ignition Sources: ATEX Zone 1 implies potential ignition sources are present.
• Consequence of Failure: Potential for fire, explosion, personnel injury, environmental damage.

SIL/PF Determination & Safety Measures

Given the ATEX Zone 1 environment, a risk assessment should likely lead to a SIL 2 or 3 requirement (or equivalent PF level). Here's a breakdown of considerations:

• Safety I/O: Highly recommended. Safety I/O provides a hardware-based safety layer independent of the PLC, ensuring the valve closes even if the PLC fails.
• Pressure Transmitter: A safety-rated pressure transmitter is crucial. It serves as the primary safety function detecting a leak and initiating valve closure. Consider a SIL 2 or 3 rated transmitter depending on the risk assessment outcome.
• Valve: The valve should be fail-safe (closes upon loss of power or signal). A certified valve for the appropriate gas group and temperature class is essential.
• PLC: The PLC needs to be appropriately specified and programmed to handle safety functions if relied upon, but should not be the *sole* safety element.

Resources

For detailed guidance and tools:

• Siemens Safety Evaluation Tool
• Siemens Industrial Safety
• Refer to IEC 61508/61511 standards for detailed SIL determination methodologies.

Disclaimer: This information is for general guidance only. A formal risk assessment performed by qualified personnel is essential to determine the appropriate SIL/PF level for your specific application.