International Standard Bases and Safety Classification - Nuclear Power Plant Instrumentation and Control Systems for Safety and Security - page 41

• On-line calibration veriication.
• On-line detection of venture fouling.
• In situ response time testing of pressure
transmitters.
• On-line detection of clogging in impulse
lines.

of functional safety assessment and assurance are
more widely used currently.
IEC 61508 is a base for a range of safety im-
portant branches of technique. Examples of E/E/
PE are fire control systems, ship motion control
systems, railway signaling systems, automatic
safety loading crane indicators, and, of course,
NPPI&C systems.
In the standard, the notion of safety lifecycle
is introduced, it is an activity connected with
implementation of safety related systems starting
from the development of design concept till E/E/
PE systems are not usable. IEC 61508 describes
two types of requirements:

• Resistor temperature detector (RTD) and

thermocouple cross calibration.

• Response time testing of RTDs and

thermocouples.

• Testing of cables and connectors.

The outlined problem, being very important,
will not be considered in this topic. The readers,
who are interested in this problem, besides IEC
standards, should be addressed to H. Hashimian's
topics (1998, 2005, 2006).

• General control system requirements.
• Individual (separate) system requirements.

IEC Standards on Critical
Systems: Functional Safety

The standard indicates typical stages of system
lifecycle and considers safety requirements for
each of the stages.
“Functional safety” is a special case of more
general concept “safety” and is in line with “fire
safety,” “electrical safety” etc.
IEC 61508 requires that functional safety as-
sessment is made for all parts of E/E/PE system
at all lifecycle stages. This standard is a basic: it
is not only used as an independent one in some
branches of industry, but also forms a ground for
development of branch standards. In IEC 61508
the main attention is paid to computer systems.
To develop IEC 61508, later IEC 61511 (IEC,
2003) was issued: “Functional safety - Safety in-
strumented systems for process industry sector,”
consisting of three parts:

IEC 61508 “Functional safety of Electrical/Elec-
tronic/Programmable Electronic safety-related
systems” (IEC, 2008), developed by technical
committee IEC SC 65 “Industrial process mea-
surement, control and automation,” applies to
critical systems in different branches of industry.
This standard refers to a wide class of systems,
including the following types of components:
electrical (E) (e.g., electromechanical devices),
electronic (E) (e.g., nonprogrammable transistor
devices), programmable (PE) (e.g., microproces-
sors, microcontrollers, logic controllers). In IEC
61508 these components are indicated as E/E/
PE and respective systems as E/E/PE systems or
E/E/PES.
The definition of “functional safety” is given in
IEC 61508: it is a part of general safety, related to
controlled equipment and to a system that controls
it, that depends on a correct operation of E/E/PE
system important to safety, on other technologi-
cal systems important to safety and devices for
decreasing external risk. This concept and methods

• 61511-1: Framework, deinitions, system,

hardware and software requirements.

• 61511-2: Guidance for the application of

IEC 61511-1.

• 61511-3: Guidance for the determination

of the required safety integrity levels (a
degree of risk reduction, provided by the
system, is understood).