  System safety refers to a diverse engineering discipline assessing and
improving various aspects of safety in socio-technical systems and their
software-intensive sub-systems. While system safety has been a vital area of
applied research for many decades, its practice and practitioners seem
empirically still not well studied. Beyond mainly anecdotal evidence
(interviews, on-line discussions), incident reports, and surveys, we are
missing open, large-scale, and long-term investigations that promote knowledge
transfer and research validation. We explore means for work safety
practitioners rely on, factors influencing their performance, and their
perception of their role in the system life cycle. Along with that we examine
observations from previous research. We build a construct of safety practice,
collect data for this construct using an on-line survey, summarise and
interpret the collected data, and investigate several hypotheses based on the
previous observations. We analyse and present the responses of 124
practitioners in safety-critical system and software projects. Aside from other
findings, our data suggests that safety decision making mainly depends on
expert opinion and project memory, lacks evidence that safety is typically a
cost-benefit question, does not exhibit the prejudice that formal methods are
not beneficial, leaves it unclear as to whether or not standards and methods
have become inadequate, and indicates that safety is not typically confused
with reliability. Additionally, we contribute a research design directing
towards explanatory empirical studies of safety practice. Empirical research of
safety practice is still in an early stage, bearing the risk of undesirable
mismatches of the state of the art and the state of practice. However, this
situation offers great opportunities for research.
