Three appeal court judges determined that the likelihood of harm arising from the offence was low rather than medium under the sentencing guidelines and substituted the penalty imposed by Judge Martin Beddoe for a fine of £190,000.
Squibb was originally fined at Southwark Crown Court in July 2017 after it pleaded guilty to breaching s 2(1) of the Health and Safety at Work Act.
The court was told that the development and refurbishment of St Mary's primary was managed by a company called NPS London on behalf of the London Borough of Waltham Forest. NPS commissioned an asbestos survey from Redhill Analysts and appointed Mansell Construction Services (now Balfour Beatty) as the principal contractor for the work, which engaged Squibb for the demolition work.
Part of this work was carried out between 4 and 14 April 2012 during the school's Easter holidays, and resumed on 23 July the same year. The next day one of Squibb's employees was inspecting an area above a suspended ceiling when he identified suspect asbestos-containing materials. A new asbestos survey discovered "widespread" asbestos sprayed on ceilings and confirmed that parts of the school that had been demolished had contained asbestos.
An inspection by the Health and Safety Executive (HSE) found the companies did not review the original survey report in detail and failed to consider the "multitude of caveats". Balfour Beatty Regional Construction and NPS London were also convicted of safety and health breaches.
However, Squibb's lawyer, Mr Watson QC, told the appeal that Judge Beddoe's assessments of culpability and harm "had placed the offence in the wrong category", resulting in a sentence which was "manifestly excessive".
Though the senior judges said Squibb's culpability was high and that the seriousness of the harm risked was at level A, they agreed "there does not appear to us to have been any proper basis for the judge's conclusion that there was a medium likelihood of such harm arising".
They criticised Judge Beddoe for failing to explain why he disregarded scientific evidence submitted by Squibb at the trial.
Judge George Leggatt said: "The expert's best estimate was that, if 100,000 people were exposed to asbestos to a similar extent to Squibb's employees, about 90 deaths would result. To put this into context, the risk of dying from smoking cigarettes is around one in five (i.e. 20,000 cases per 100,000) and the risk of dying from working in the construction industry for 40 years or from an accident on the roads is around 500-600 chances per 100,000.
"Any estimate of the kind which he made can only be very rough. Long-term risks of this nature are inherently difficult to assess and quantify, the relevant scientific knowledge is far from perfect and any estimate must be subject to a wide margin of error. But that is not a reason to reject or disregard whatever scientific evidence is available. The rational approach for a court to adopt in these circumstances is to rely on the best evidence that is has."
He added: "We see no justification for assessing the likelihood of harm in this case as medium. The only reasonable conclusion on the available evidence was that the likelihood of harm arising from the offence was low."
They concluded that the offence fell in harm category 3, for which the starting point for an offence involving high culpability committed by a medium-sized organisation is £210,000. They then made a 10% downward adjustment to take account of mitigating factors.