Seven police officers were doused with ammonia while dealing with a report of a domestic incident in Lancashire, leaving one seriously ill in hospital.
The sergeant, from Lancashire Police, was among seven officers sprayed with cleaning liquid while on the call in Ash Grove, in Darwen, in the early hours of Tuesday.
He suffered serious injuries to his eyes, throat and respiratory system and is being treated in Royal Blackburn Hospital. The six other officers have been discharged.
The alleged attacker, a man aged 46, escaped through a first-floor window but has since been arrested on suspicion of grievous bodily harm with intent.
Superintendent Andrea Barrow said: "This shocking incident from the early hours of the morning has left an officer with some significant and serious injuries.
"My thoughts are with him and his family and I wish him a speedy recovery and look forward to his return to work.”
Lancashire Chief Constable Andy Rhodes added: "My thoughts are with this officer and all of those affected by this incident, which shows once again the dangers that officers face and how they put their lives on the line each and every day to protect people."
