The Police Ombudsman has accepted an invitation from the PSNI to investigate each use of CS spray by its officers.
Mrs Nuala O'Loan told delegates to the annual conference of the Police Federation, which represents the majority of officers, that she would only monitor incidents involving the spray for three months. She said the workload faced by her investigative team and the resources available to them meant all incidents could not be monitored indefinitely.
Mrs O'Loan's office already investigates every use of plastic bullets in Northern Ireland, although none has been fired in the two years since Mr Hugh Orde became chief constable.
CS spray is used to incapacitate individuals by officers dealing with disorder. The sprays are not designed for general usage in crowd-control situations.
Her statement to the Police Federation was made during a private session of the conference in Newcastle, Co Down.
The Police Ombudsman's office has pressed for additional resources to meet the demands made on it since it was established in 2000.
Mrs O'Loan has a staff of 128 including 90 investigating officers, some of whom are seconded from police forces in Britain. The office has an annual budget of £7 million and has investigated 12,723 cases in the past three years and 10 months.
Mrs O'Loan also rejected complaints that her officers were too ready to arrest PSNI members in the course of investigations.
The Irish Times was told that only 16 officers have been arrested to date, all of them "by appointment", and that four convictions have flowed from such arrests. Sixteen prosecutions were ordered by the DPP.
The Police Ombudsman's office is only one of a plethora of agencies which have watchdog responsibilities in relation to the PSNI.
The chief constable says his service is the most scrutinised in the western world, and is subject to investigation by Mrs O'Loan, Her Majesty's Inspectorate of Constabulary, the Police Oversight Commissioner and a range of other outside bodies with both general and specific remits.
The oversight commissioner is due to release his next report on the implementation of the Patten Commission recommendations on Tuesday.
Despite the public falling-out in 2002 between Mrs O'Loan and Sir Ronnie Flanagan, the former chief constable, over the handling of the Omagh investigation, a source said yesterday's proceedings were cordial.