An important decision on industrial disease.
At pages 415–416, having cited Stokes, Mustill J. said,
In the passage just cited, Swanwick J. drew a distinction between a recognised practice followed without mishap, and one which in the light of common sense or increased knowledge is clearly bad.
The distinction is indeed valid and sufficient for many cases.
The two categories are not, however, exhaustive: as the present actions demonstrate.The practice of leaving employees unprotected against excessive noise had never been followed ‘without mishap.’Yet even the plaintiffs have not suggested that it was ‘clearly bad,’ in the sense of creating a potential liability in negligence, at any time before the mid-1930s.
Between the two extremes is a type of risk which is regarded at any given time (although not necessarily later) as an inescapable feature of the industry.
The employer is not liable for the consequences of such risks, although subsequent changes in social awareness, or improvements in knowledge and technology, may transfer the risk into the category of those against which the employer can and should take care.
It is unnecessary, and perhaps impossible, to give a comprehensive formula for identifying the line between the acceptable and the unacceptable. Nevertheless, the line does exist, and was clearly recognised in Morris v West Hartlepool Steam Navigation Co Ltd  AC 552 . The speeches in that case show, not that one employer is exonerated simply by proving that other employers are just as negligent, but that the standard of what is negligent is influenced, although not decisively, by the practice in the industry as a whole.
In my judgment, this principle applies not only where the breach of duty is said to consist of a failure to take precautions known to be available as a means of combating a known danger, but also where the omission involves an absence of initiative in seeking out knowledge of facts which are not in themselves obvious.
The employer must keep up to date, but the court must be slow to blame him for not ploughing a lone furrow.
Formatting changed for ease of reading.
Thompson v Smith was cited with approval in Baker v Quantum  UKSC 17.