Functional safetyGeneral information

Contents

What is functional safety?

First the definition of safety. This is freedom from unacceptable risk, directly or indirectly, of physical injury or damage caused to the health of people, to equipment and to the environment

The functional safety of a system is part of the overall safety that depends on another system or equipment operating correctly in response to its inputs.

For example, an over temperature protection device, using a thermal sensor in the winding of an electric motor to de-energise the motor before overheating, is an instant of functional safety.
But providing specialised safety winding insulation to withstand high temperature is not an instance of functional.

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Safety standards

L'The objective of these standards is to classify the industrial sites according to their risks:

• according to the human aspect (wounded, killed person)
• according to the environmental aspect (emission of gas, fuel oil, ... outside)
• according to the financial aspect (repair, maintenance, immobilization, damage to property)

International standards:	IEC 61508 & IEC 61511
IEC 61508	Functional safety of Electrical/Electronic/Programmable electronic (E/E/EP) Safety Related Systems (1998).
IEC 61511	Functional safety of Safety Instrumented Systems for the process industry.

SIL levels

The required Safety Integrity Level (SIL) for a safety system loop depends on the effect on people, environment and equipment if it fails to operate when it should. In the IEC standard 4 different SIL levels are defined:

• Level 1 : SIL1: Minor property and production protection
• Level 2 : SIL2: Major property and production protection (possible people injury)
• Level 3 : SIL3: Employee and community protection
• Level 4 : SIL4: Catastrophic community impact

The level SIL (n) means that the Probability of Failure on Demand (PFD) is between : 10-(n+1) ≤ PFD < 10-n.

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The safety system

A safety system loop or Safety Instrumented System (SIS) consists out of a 3 part-architecture:

Safety system Sensor sub-system (sensors & input interface) Logic solvers sub-system Final element sub-system (output interface & final elements) Each sub-system has its own PFD value. The total PFD of the sub-systems must satisfy the SIL value defined for the site

For example

LThe diagram above shows a typical safety loop in the process industry. The spool valve and the process valve are parts of the final element. If the sensor detects a too high safety level, the PLC gives a signal to the pilot valve which closes the process valve.

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ASCO NUMATICS offer

ASCO NUMATICS obtained the TÜV approval for 3 products.

• solenoid valves series 327 (PFD <4x10^-7) and series 126 (PFD <8x10^-7)
• spool valves series 551 (PFD <4x10^-7)
• these products are approved to be used on SIL 4 safety loop (highest level).

These products received the TÜV approval with their exhaust protector (silencers connected to the product exhaust port). They will not be approved any more if the end user dismounts or changes the exhaust protector. This modification is under the responsibility of the user.

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Certificates

The ASCO NUMATICS products were executed with the TÜV in Germany.
Download the certificates:

• TÜV S 19402 certificate for the series 327 solenoid valves
• TÜV V 72 2005 T1 certificate for the series 126 solenoid valves
• TÜV V 24 2003 T1 certificate for the series 551 spool valves