14. Presentation - Safety System Design

ENG / SERVICES

Machinery SafetySafety System Design

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Purpose

The purpose of this module is to give you an understanding of the process of safety system design.

After this session you will:• Be able to identify the two international standards related to

interlocks and safety related control systems• Have a basic understanding of the ISO 13849-1 process for defining

the required Performance Level (PL) of a safety related control system

Note: This session is not intended to give you the specialist skills to design a safety related control systems. Persons with these skills may be available in your MES E&A group and are available from external consultants, e.g. Rockwell.

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Machinery Safety – Control Systems EN 954-1 S Severity of Injury S1 = Slight (normally reversible) injury S2 = Serious (normally irreversible) injury, including

death F Frequency and/or duration of exposure to the

hazard F1 = Seldom to quite often and/or short exposure

time F2 = Frequent to continuous and/or long exposure

time P Possibility of avoiding the hazard P1 = Possible under specific conditions

P2 = Nearly impossible Circuit Category

B = Basic, Able to operate under expected conditions

1 = B + Proved components and safety principles

2 = B + Proved safety principles + tested at appropriate intervals

3 = B + Proved safety principles + a single fault does not lead to loss of safety function + if possible, individual faults should be detected

4 = B + Proved safety principles + a single fault in each of these parts does not lead to loss of safety function + individual faults are detected before the next safety function

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SUPERCEDED

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New Standards

EN 62061 – Safety of Machinery• “Functional safety of safety related electrical,

electronic and programmable electronic systems”• Applies only to electrical control systems• International Electrotechnical Commission

ISO 13849-1 – Safety of Machinery• “Safety related parts of control systems –

principles for design”• Applies to all types of control systems – electrical,

pneumatic, mechanical, hydraulic• Uses the same categories for defining the system

structure as EN 954-1, i.e. B,1,2,3 and 4.• International Organisation for Standardisation (ISO)

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ISO 13849 Working Method (Simplified)

Determine the System Scope(space, usage, time, environment)

Identify the Risk Sources(all work operations during the life cycle)

Estimate the Risk(determine PL with S, F and P)

Evaluate the Risk(Is action required?)

Reduce the Risk(Avoid, Protect/Safety Devices,

Information)

Identify the Safety Functions

Determine PLr(Often from Risk Estimate)

Design and implement the solution for the safety function

Calculate the PL

START

END

Verify that PL ≥ PLr

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PLr = Performance Level required to manage the Risk Source – How significant is the risk and therefore what “risk reduction performance” does the solution need to have.

S Severity of injury• S1 Slight (normally reversible, bruises, abrasions,

puncture wounds, minor crushing injuries)• S2 Serious (normally irreversible or death, skeletal

injuries, amputations, death)

F Frequency and/or exposure to hazard

• F1 Seldom to less often and/or exposure time is short (less than once per hour)

• F2 Frequent to continuous and/or exposure time is long (more than once per hour)

P Possibility of avoiding hazard or limiting harm

• P1 Possible under specific conditions (slow machine movements, plenty of space, low power)

• P2 Scarcely possible (quick machine movements, crowded, high power)

Calculate the PLr

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Information)




Calculate the PL

START

END


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Eliminate the Risk

Elimination(completely remove the hazard)

Substitution(substitute a hazardous machine or process with a non hazardous one)

Engineering(guarding, enclosure, automation)

Administration(Training, SOP’s, reducing number and time of

exposure, LOTO, signs)

PPE(Avoid, Protect/Safety Devices, Information)

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Information)




Calculate the PL

START

END


Determine PLrequired(Often from Risk Estimate)

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PLr = Required Performance Level for the remaining Risk Source

S Severity of injury• S1 Slight - normally reversible (bruises, abrasions,

puncture wounds, minor crushing injuries)• S2 Serious - normally irreversible or death (skeletal

injuries, amputations, death)

F Frequency and/or exposure to hazard

• F1 Seldom to less often and/or exposure time is short (less than once per hour)

• F2 Frequent to continuous and/or exposure time is long (more than once per hour)

P Possibility of avoiding hazard or limiting harm

• P1 Possible under specific conditions (slow machine movements, plenty of space, low power)

• P2 Scarcely possible (quick machine movements, crowded, high power)

Calculate the PLr

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Information)




Calculate the PL

START

END


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Safety Function

Interlock Switch Safety Relay Redundant monitored contractors Line stops

Light curtain Safety Relay Redundant monitored contractors Line stops

Emergency Stop 1 Safety Relay Redundant monitored contractors Line stops

Emergency Stop 2 Identical to Emergency Stop 1 so no need to calculate

Two hand device Safety PLC Machine stop input to robot, redundant Robot stops

Light curtain Safety PLC Machine stop input to robot, redundant Robot stops

Non contact sensor Safety PLC Machine stop input to robot, redundant Robot stops

INPUT LOGIC OUTPUT RESULT

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Information)




Calculate the PL (of the Safety Solution)

START

END


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Calculate PL of the safety function (simplified)

Safety Function Design

ComponentArchitecture

(Category B,1,2,3 or 4)

DiagnosticCoverage

Common Cause Failure

B Basic, Able to operate under expected conditions1 B + Proved components and safety principles2 B + Proved safety principles + tested at appropriate

intervals3 B + Proved safety principles + a single fault does

not lead to loss of safety function + if possible, individual faults should be detected

4 B + Proved safety principles + a single fault in each of these parts does not lead to loss of safety function + individual faults are detected before the next safety function

Nil <60%Low >60% to <90%Medium >90% to <99%High >99%

DiversitySeparationElectromagnetic compatibilityProtection against pollution

PLPerformance Level

MTTFMean Time to Failure

Nil <60%Low >60% to <90%Medium >90% to <99%High >99%

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Calculate PL of the safety function (not simplified !!)

USE A SPECIALIST

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Information)




Calculate the PL

START

END


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Questions?

14. Presentation - Safety System Design

Documents

Transcript of 14. Presentation - Safety System Design