Police forces were effectively banned from using a restraint belt across the faces of detainees following the death of Thomas Orchard.
The 32-year-old church caretaker died in hospital seven days after being restrained at Heavitree Road police station in Exeter, Devon, in October 2012.
On Tuesday, a jury at Bristol Crown Court found a custody sergeant and two detention officers who dealt with Mr Orchard not guilty of his manslaughter by gross negligence.
Devon and Cornwall Police is being investigated for potential charges of corporate manslaughter and offences under the Health and Safety at Work legislation.
Following Mr Orchard's death, the Independent Police Complaints Commission (IPCC) wrote to every police force expressing concern about ERB use about the head.
Bristol Crown Court was told that the policy of at least one force - Northamptonshire - offered the ERB as an option to prevent spitting or biting until May 2013.
It is understood that the force did not routinely use the ERB for this purpose from Mr Orchard's death until the policy changed, when spit hoods were introduced.
The Press Association used the Freedom of Information Act to ask every police force in the UK about their use of the ERB before and after Mr Orchard's death.
:: Six forces continue to use the US-made device but this is only as a limb restraint or carrying aid and not around the head
:: Four forces used the ERB to protect officers from spitting and biting at the time of Mr Orchard's death
:: The vast majority of forces never used the ERB
Mr Orchard, who had paranoid schizophrenia, was experiencing a mental health crisis when he was arrested in Exeter city centre at 11am on October 3 2012.
He was handcuffed and restrained around his legs before being driven to the Heavitree Road custody unit, where an ERB was wrapped around his face.
Custody sergeant Jan Kingshott, 45, and detention officers Simon Tansley, 39, and Michael Marsden, 56, were on duty at the time.
They insisted the use of the belt was proportionate and lawful, claiming that Mr Orchard was persistently threatening to bite them.
A jury at Bristol Crown Court acquitted Sgt Kingshott, Mr Tansley and Mr Marsden of Mr Orchard's manslaughter by gross negligence following a six-week trial.
Mr Orchard's cause of death was severe hypoxic-ischemic brain damage, caused by a prolonged cardio-respiratory arrest following a violent struggle and period of physical restraint.
In a statement, a spokeswoman for the National Police Chiefs' Council (NPCC) said: "The NPCC does not condone the use of ERB as an improvised spit hood and the guidance issued to forces is for it only to be used as a limb restraint."
Devon and Cornwall Police had authorised the US-made restraint device for use across the face to prevent spitting or biting.
A risk assessment by the force did not identify or refer to any risks to detainees when the belt was used around the head.
Custody records show the force used the ERB around a detained person's face 55 times in the 12 months up to and including Mr Orchard's detention.
Graham Cook, a medical advisor, said he was asked to evaluate the safety of the belt when used about the head for Kent Police and viewed a demonstration.
His report, from 2001, highlighted concerns the ERB could partially obstruct the airway, make it difficult to detect respiratory problems and was dangerous.
In an interview with Channel 4 News, Mr Cook said: "It was in my medical view that it should not be used in this manner because it was extremely likely to cause significant injury or even death to the person."
The force never used the device about the head.
A spokesman for the IPCC confirmed that the "corporate decision-making" by Devon and Cornwall Police about the ERB was under investigation.
"Investigators are conducting detailed analysis to fully understand the force's policies and processes governing its use," he said.
"In addition, an independent expert with a background in health and safety has been instructed in relation to this matter."
Sgt Kingshott, Mr Marsden and Mr Tansley, and four other Devon and Cornwall Police officers who were involved in Mr Orchard's arrest and restraint still face potential disciplinary proceedings for gross misconduct.
In a statement issued after the verdicts, Chief Constable Shaun Sawyer said: "There remains further considerations by the Independent Police Complaints Commission.
"We now await further information and direction from them on this matter.
"Additionally, there will be further investigation by them and the Health and Safety Executive into corporate matters, with which the force has co-operated.
"As the corporate head, in my role as Chief Constable, I await decisions from them and the Crown Prosecution Service.
"I am not able to say any more in respect of those matters."