Situated in critiques of the “moral muteness” of technical rationality, we examine concepts of ethics and the avoidance of ethical language among Australian gas pipeline engineers. We identify the domains in which they saw ethics as operating, including public safety, environmental protection, sustainability, commercial probity, and modern slavery. Particularly with respect to ethical matters that bear on public safety, in the course of design and operational activities, engineers principally advocated for action using technical language, avoiding reference to potential consequences such as death or destruction of property. Within their organizations, they saw themselves as occupying a technical “line of defense”. We argue that this focus on technical language is action-oriented. Ethics tells practitioners of unacceptable outcomes, but it does not guide them in what they need to do to avoid that outcome in practice. We observed some cases where engineers had not made the connection between their role and ethics in the sense of public safety. We argue that muteness on ethical matters can obscure the nature of the risk where technical advice is being taken on by non-technical actors, and where technical actors themselves do not have a clear sense of their public safety obligations.