A police force may have failed to properly assess a restraint belt that was placed across the face of a church caretaker before he collapsed in custody in 2012, a court has been told.

Thomas Orchard, 32, who had paranoid schizophrenia, died in hospital seven days after being arrested and taken to a police station in Exeter.

In a landmark conviction last year, the office of the chief constable of Devon and Cornwall police admitted breaches under the Health and Safety at Work Act over Orchard’s death.

A trial of issue is taking place at Bristol crown court before Judge Julian Lambert to resolve a series of disputed matters, including whether the use of the heavy webbing emergency response belt (ERB) was a contributory factor in the death.

Mark Heywood QC, prosecuting, told the court there were a number of failings in the way the force procured, assessed, reviewed and trained staff how to use the device.

He said the ERB was first approved for use by the force as a limb restraint in a custody setting in 2002 but was being “in practice” used as a spit or bite guard within months.

“It doesn’t appear that any risk assessment was carried out for this particular use of the ERB,” Heywood told the judge. “This is a fundamental failing and may [be] or is capable of explaining all the other problems that follow.”

After Orchard’s death in October 2012, laboratory tests were carried out on the US-made belt.

The belt formed a “seal” around the mouth of a dummy head when wet and in a certain position. Orchard’s saliva was found on the device. The material restricted airflow more than tea towels, overalls, a handkerchief and dust masks.

Placing the ERB over a person’s face from forehead to chin with limited pressure would “to an extent” obstruct access to airflow, Heywood said.

In a 2001 report – 11 years before Orchard’s death – Dr Graham Cook raised concerns that the device could partially obstruct a person’s airway if used about the head.

This report was referenced in a memo written by a Devon and Cornwall police custody training officer in April 2002, as well as other documents about the ERB.

Heywood said the force only initially approved the belt for use as a limb restraint but within months it was adopted as a spit or bite guard.

“Without policy guidelines in place, without any assessment in place, without any controls in place, custody units were already using the belt for this purpose at that time,” he said.

In February 2003, the custody training officer wrote an email saying he had demonstrated the “hooding” capabilities of the ERB to a colleague, the court was told.

“The reference to the word ‘hooding’ is of some significance because historically it has been avoided by the security services and police forces of this country,” Heywood said.

The force’s policy for the belt was updated in April 2003, stating it could be “held loosely about the head” to deal with headbutting, biting or spitting.

Orchard was arrested after a disturbance in Exeter in October 2012 and taken to the city’s Heavitree Road police station. During his detention, an ERB was placed across his face.

The force does not accept the belt caused Orchard’s death. It admitted breaching health and safety law on the basis that there were failings over issues such as how officers were trained.

The trial of issue, due to last up to four days, continues. The force will be sentenced next month.