A trial of spit hoods by Humberside Police is to be extended across the whole force area.
During the initial pilot, which lasted three months, selected officers were issued with guards to prevent suspects spitting and biting.
Ch Insp Paul Butler said the extension would help gather further evidence on the effectiveness of spit guards in dealing with difficult detainees.
The force said the fabric mesh guards would only be used on rare occasions.
A quarter of all assaults on officers are as a result of being spat at, or bitten, it said.
Talking about the scheme, Ch Insp Butler said: "We are confident that this will give us more evidence and a better understanding of how the spit guards would work across the force to protect those involved in handling extremely difficult detainees."
He said the extension includes all custody suites and one team in each of our four geographical areas: Hull, east Yorkshire, northern Lincolnshire and north-east Lincolnshire.
Humberside Police said it had used spit hoods twice during the initial pilot scheme, with the process being recorded and reviewed, and put before an independent scrutiny panel.
Ch Insp Butler said the force would review any evidence before making a decision on a further roll-out of the guards. The extended pilot will run for three months.
In November, a BBC freedom of information request found they were in use by 17 of the 49 UK police forces.
Campaign group Liberty previously described the guards as "a primitive, cruel and degrading tool", but the Police Federation said they "should be available as standard".
What are spit guards/hoods?
Mesh fabric hoods placed over the heads of suspects to prevent spitting or biting.
They can only be used once and are usually used in custody suites or when moving people in custody from one location to another.
Critics say spit hoods are distressing, humiliating and can cause panic.
Forces say they only use the hoods when "proportionate, appropriate and justifiable" to protect their officers.