
\paragraph{Abstract}{
The ability to assess the safety of man made equipment has been a concern 
since the dawn of the industrial age~\cite{indacc01}~\cite{steamboilers}.
The philosophy behind safety measure has progressed
with time, and by world war two~\cite{boffin} we begin to see concepts such as `no single component failure should cause
a dangerous system failure' emerging.
The concept of a double failure causing a dangerous condition being unacceptable,
can be found in the legally binding European standard EN298~\cite{en298}.
More sophisticated statistically based standards, i.e EN61508~\cite{en61508} and variants thereof,
governing failure conditions and determining risk levels associated with systems.

All of these risk assessment techniques are based on variations on the theme of 
Failure Mode Effect Analysis (FMEA), which has its roots in the 1940's mass production industry
and was designed to save large companies money by fixing the most financially
draining problems in a product first.

This thesis show that the refinements and additions made to
FMEA to tailor them for military or statistical commercial use, have common flaws 
which make them unsuitable for the higher safety requirements of the 21st century.
Problems with state explosion in failure mode reasoning and the impossibility
of integrating software and hardware failure mode models are the most obvious of these. %flaws.
The methodologies are explained in chapter~\ref{sec:chap2} and the advantages and drawbacks
of each FMEA variant are examined in chapter~\ref{sec:chap3}.
In chapter~\ref{sec:chap4}, a new methodology is then proposed which addresses the state explosion problem
and, using contract programmed software, allows the modelling of integrated
software/electrical systems.
This is followed by two chapters showing examples of the new modular FMEA analysis technique (Failure Mode Modular De-Composition FMMD)
firstly looking at electronic circuits and then at electronic/software hybrid systems.
}

\section{Introduction}

Msc project Euler/Spider Diagram editor --- Euler/Spider Diagrams
could be used to model failure modes in components.
--- 2005 paper --- need for static analysis because of
high reliability of modern safety critical systems.

\section{Practical Experience: Safety Critical Product Approvals}

FMEA performed on selected areas perceived as critical
by test house.
Blanket measures, RAM ROM checks, EMC, electrical and environmental stress testing

\subsection{Practical limitations of testing for certification vs. rigorous approach}

State explosion problem considering a failure mode of a given component against
all other components in the system i.e. an exponential ($2^N$) order of processing resource rather than a polynomial i.e. $N^2$.

Impossible to perform double simultaneous failure analysis (as demanded by EN298~\cite{en298}).

