System safety

System safety, 2013

Slide 1
Safety
• Safety is a property of a system that
reflects the system’s ability to
operate, normally or abnormally, without
d...
Principal dependability
properties

System safety, 2013

Slide 3
Safety criticality
• Primary safety-critical systems
– Embedded software systems whose
failure can cause the associated
ha...
System safety 2013

Slide 5
• Secondary safety-critical systems
– Systems whose failure results in faults in other
(socio-technical) systems, which ca...
System safety 2013

Slide 7
Safety and reliability
• Safety and reliability are related but
distinct
• For a system to be safe, it must
generally be r...
• Reliability is concerned with
conformance to a given specification
and delivery of service
• Safety is concerned with en...
• A reliable system can be unsafe if the
requirements are incorrect or
incomplete

System safety 2013

Slide 10
Unsafe reliable systems

The software on this plane operated ‘reliably’ yet the plane
crashed- covered in a separate video...
Unsafe reliable systems
• There may be dormant faults in a system
that are undetected for many years and
only rarely arise...
• Hardware failures generating spurious inputs
– Hard to anticipate in the specification.

• Context-sensitive commands i....
Accident
• An unplanned event or sequence of events
which results in human death or
injury, damage to property, or to the
...
Hazard
• A condition with the potential for causing or
contributing to an accident. A failure of the
sensor that measures ...
Damage
•

A measure of the loss resulting from a mishap.
Damage can range from many people being killed as
a result of an ...
Safety critical systems
development
• Hazard avoidance
– The system is designed so that some
classes of hazard simply cann...
• Hazard detection and removal
– The system is designed so that hazards are
detected and removed before they result in
an ...
• Damage limitation
– The system includes protection features
that minimise the damage that may result
from an accident.

...
Summary
• Safety is a property of a system that reflects
the system’s ability to operate, normally or
abnormally, without ...
Summary
• Hazards are conditions that may (but need
not) lead to an accident
• Safety is achieved through
– Hazard avoidan...
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System safety

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Transcript of "System safety"

  1. 1. System safety System safety, 2013 Slide 1
  2. 2. Safety • Safety is a property of a system that reflects the system’s ability to operate, normally or abnormally, without danger of causing human injury or death and without damage to the system’s environment. System safety, 2013 Slide 2
  3. 3. Principal dependability properties System safety, 2013 Slide 3
  4. 4. Safety criticality • Primary safety-critical systems – Embedded software systems whose failure can cause the associated hardware to fail and directly threaten people. System safety 2013 Slide 4
  5. 5. System safety 2013 Slide 5
  6. 6. • Secondary safety-critical systems – Systems whose failure results in faults in other (socio-technical) systems, which can then have safety consequences. – For example, a medical records system is safetycritical as failure may lead to inappropriate treatment being prescribed. System safety 2013 Slide 6
  7. 7. System safety 2013 Slide 7
  8. 8. Safety and reliability • Safety and reliability are related but distinct • For a system to be safe, it must generally be reliable • However, this is not enough. It must also be safe in the event of system failure System safety 2013 Slide 8
  9. 9. • Reliability is concerned with conformance to a given specification and delivery of service • Safety is concerned with ensuring system cannot cause damage irrespective of whether or not it conforms to its specification System safety 2013 Slide 9
  10. 10. • A reliable system can be unsafe if the requirements are incorrect or incomplete System safety 2013 Slide 10
  11. 11. Unsafe reliable systems The software on this plane operated ‘reliably’ yet the plane crashed- covered in a separate video System safety 2013 Slide 11
  12. 12. Unsafe reliable systems • There may be dormant faults in a system that are undetected for many years and only rarely arise. • Specification errors – If the system specification is incorrect then the system can behave as specified but still cause an accident. System safety 2013 Slide 12
  13. 13. • Hardware failures generating spurious inputs – Hard to anticipate in the specification. • Context-sensitive commands i.e. issuing the right command at the wrong time – Often the result of operator error. System safety 2013 Slide 13
  14. 14. Accident • An unplanned event or sequence of events which results in human death or injury, damage to property, or to the environment. • An overdose of insulin by a softwarecontrolled insulin injection system is an example of an accident. System safety 2013 Slide 14
  15. 15. Hazard • A condition with the potential for causing or contributing to an accident. A failure of the sensor that measures blood glucose is an example of a hazard. System safety 2013 Slide 15
  16. 16. Damage • A measure of the loss resulting from a mishap. Damage can range from many people being killed as a result of an accident to minor injury or property damage. • Damage resulting from an overdose of insulin could be serious injury or the death of the user of the insulin pump. System safety 2013 Slide 16
  17. 17. Safety critical systems development • Hazard avoidance – The system is designed so that some classes of hazard simply cannot arise. System safety 2013 Slide 17
  18. 18. • Hazard detection and removal – The system is designed so that hazards are detected and removed before they result in an accident. System safety 2013 Slide 18
  19. 19. • Damage limitation – The system includes protection features that minimise the damage that may result from an accident. System safety 2013 Slide 19
  20. 20. Summary • Safety is a property of a system that reflects the system’s ability to operate, normally or abnormally, without danger of causing human injury or death. • Safety and reliability are related but reliable systems may be unsafe. System safety 2013 Slide 20
  21. 21. Summary • Hazards are conditions that may (but need not) lead to an accident • Safety is achieved through – Hazard avoidance – Hazard detection and removal – Damage limitation System safety 2013 Slide 21
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