However, civil liberties campaigners contend that all too frequently, and despite these guidelines, some police officers are "spraying suspects first and asking questions later" in situations where there is no real threat of violence being used against them.
In May, a small group of animal rights activists, many of them women, gathered to protest at the gates of a live animal exporter, Gilders, based near Cheltenham, Gloucestershire. A confrontation with police followed and, according to Gloucestershire police, CS spray was used by officers for their own protection, in accordance with Acpo guidelines.
Twenty people were arrested but all were released later without charge. The protesters, however, allege the police used the CS spray on the group indiscriminately and that they lost their self control when there was no threat of violence.
They also claim that police failed to follow proper procedures in the aftermath of CS spray use. While Acpo says the effects of CS spray dissipate after half an hour, protesters claim they were in considerable pain for days after being sprayed.
Several have now begun legal proceedings for damages against Gloucestershire police, and are using video and photographic evidence recorded at the disturbance. Two protesters (whose names have been changed because of the pending legal action) told their version of events to the Independent on Sunday.
"James", 27, said: "I was just walking down the road by the perimeter fence when a policeman barred my way and said, `You can't go any further' and before I could say anything he sprayed me straight in the face.
"I put my hand up to protect my face but he pulled it away and held on to my arm and squirted me again several times.
"It was really painful. I used to be in the military and we did experiments with CS gas, but this stuff was much stronger. My eyes were burning and streaming. I was blinded for five minutes. I couldn't breathe - some people with asthma had to go to hospital - and the spray stuck to my skin.
"You really want to rub your eyes, but you can't because it makes it worse. For hours afterwards my eyes were watering. The vapours were on my clothes and it was so strong that later I was travelling in a car and my companions were also affected.
"The next day I had really bad diarrhoea. I had dreadlocks at the time so I couldn't wash the CS out of my hair. For a week I was scratching my head - it was torture. In the end, I had to shave all my hair off."
"Susie", 24, said: "We were cornered up against a fence and the police were just spraying it all over us. I was held down by two police officers and they sprayed me twice. Immediately there was a really bad stinging in my eyes. I couldn't breathe; my throat was burning - it was the worse thing you can imagine. I started going into a panic and I was crying.
"The police didn't care and I was handcuffed and laid on the floor of a van. The didn't let me breathe fresh air. They didn't even open a window. I was held in a cell for 30 hours and the spray was still on my clothes and in my hair and my eyes were still stinging. They didn't call a doctor and in the end I had to ask for one, but he was no help.
"CS is really toxic. I still get a rash on my face where it hit. Some landed on my navy jumper and turned it purple. When I was released I went to the hospital. I asked, `What damage can the spray do to my insides if it can take the colour out of my top?' and the doctor said, `We don't know'."Reuse content