The recent case of R v Wood Limited Treatment highlights the problems faced by prosecution authorities in proving causation for the purposes of establishing criminal liability for corporate manslaughter.


This case concerned the tragic events at Bosley Mill (‘the Mill’) where on 17 July 2015 a large explosion resulted in the deaths of four workers. The Mill produced wood dust, which is defined as a “dangerous substance” under Regulation 2(c) of the Dangerous Substances and Explosive Atmospheres Regulations 2002 and known to be explosive in certain conditions.

Following this incident, the company, Wood Treatment Limited (‘WTL’), and its Director, George Boden, were prosecuted for corporate manslaughter and gross negligence manslaughter respectively, as well as for further offences under health and safety legislation.

At the trial, it was common ground that the explosion was caused by the ignition of wood dust in the air and that there was evidence from which a jury could conclude that the risk of explosion was much higher than it should have been because of the negligence of WTL and Mr Boden.

Section 58 appeal

At the end of the prosecution case, the trial judge, Mrs Justice May, ruled in favour of the Defendant’s submission of no case to answer in respect of the manslaughter offences (‘the terminating ruling’). The prosecution appealed this ruling under section 58 of the Criminal Justice Act 2003 (‘CJA’), which allows the prosecution to appeal a ruling in relation to a trial on indictment at an “applicable time”, meaning any time before the judge starts their summing-up to the jury. In order to initiate the appeal, the prosecution must inform the court that it intends to appeal and request an adjournment (s.58(4) CJA). At the time of informing the court of its intention to appeal, the prosecution must also enter into an ‘acquittal agreement’ providing that it agrees the defendant(s) should be acquitted if leave to appeal is not obtained, or if the appeal is abandoned before it is determined (s.58(8)-(9) CJA).

In this case, leave to appeal was granted and the trial was adjourned whilst the appeal was determined by the Court of Appeal. The question on appeal was whether the trial judge was right to conclude that there was insufficient evidence to prove that the negligent acts or omissions alleged against WTL and Mr Boden played a substantial part in causing the explosion.


The offence of corporate manslaughter requires an organisation to manage or organise its activities in such a way that causes a person’s death and amounts to a gross breach of a duty of care owed to the deceased. Furthermore, an organisation is guilty of corporate manslaughter only if the way in which its activities are managed or organised by its senior management is a substantial element of that breach.

This case presented evidential challenges in terms of proving the cause of the explosion, as since the explosion had largely destroyed the Mill there was little psychical evidence available. At trial, a joint expert statement posited four possible causative scenarios for the explosion. Scenarios 1, 2 and 4 relied on the accumulation of wood dust which had previously settled within the Mill and then ignited. During the trial there had been evidence that the Mill was dusty, with wood dust settled across surfaces which had not been adequately cleaned, and that leaks from the poorly designed and maintained machinery had also produced dust. The prosecution case was that negligent failures of management had resulted in the accumulation of wood dust in dangerous quantities which had then caused the explosion.

However, scenario 3 did not rely on the accumulation of dust and instead suggested the explosion may have been caused following a large release of wood dust from a faulty piece of equipment. The Court of Appeal held that, given scenario 3 could not be ruled out as a potential cause of the explosion, prosecution evidence about accumulations of dust could not prove the necessary causal link between the fault and the explosion. In order to make such a causal link, it would be necessary to also examine scenario 3 and adduce evidence of the extent to which it involved the negligence of WTL and Mr Boden, but that had not been done by the prosecution.

The Court of Appeal upheld the trial judge’s ruling of no case to answer on the basis that it was impossible for the jury to exclude all realistic possibilities for the explosion consistent with the innocence of the defendants. An order was made under s.61(3) CJA that the defendants be acquitted of the manslaughter offences which had been subject to the appeal.


After being acquitted of the manslaughter charges, Boden pleaded guilty to being a director of a company which committed an offence under the Health and Safety at Work Act 1974 (‘HSWA’) for which he was fined £12,000 and was barred from holding the position of company director for four years. The company, which had previously pleaded guilty to an offence of failing to ensure the health and safety of employees, was fined £75,000. Two further managers of WTL, indicted for health and safety offences, were acquitted. The court heard that prosecution costs in the case amounted to £540,000.

This case serves as a stark reminder of the difficulty in proving the causation element of corporate and gross negligence manslaughter offences. Not only must prosecutors adduce evidence in support of causes that are consistent with a manslaughter charge, but they must also address other possible causes so as to exclude them. To fail to do so means that a jury has no way to satisfy itself that such innocent explanations can be excluded from consideration making an acquittal the only possible outcome.