Some masks protecting healthcare staff against coronavirus were not properly tested, Northern Ireland’s Public Health Agency (PHA) has said.
UK fitting requirements were not followed by an independent contractor but any risk to staff is likely to be low, the PHA added.
It has been asked by the Department of Health to undertake a serious adverse incident review.
The agency said: “Additional measures across the health and social care system will be put in place to review and monitor fit-testing outcomes moving forward.
“Staff impacted will be informed and offered support.
“Fit-testing will be carried out under the correct Northern Ireland setting.”
The contractor which tested masks on some occasions inadvertently applied a fit-testing setting not normally used in Northern Ireland, the PHA said.
It said this should have been readjusted to the UK fit-testing requirements designed to prevent leaks.
The PHA added: “We fully recognise that the issues raised may cause some concern and we very much regret that.
“We would again stress that these checks are being taken as a precautionary step to reassure staff that the masks are being fitted to the highest safety standards.
“Rigorous tried and tested procedures have been in place during the pandemic for staff to highlight any concerns if they feel their PPE equipment does not properly fit.”
The rate of spread of the infection has fallen significantly in recent weeks in Northern Ireland and groups of up to six people can now meet indoors.
One more death in the North was reported on Tuesday.
Meanwhile, new guidance was published which will enable the tourism and hospitality sectors to open as safely as possible, economy minister Diane Dodds said.
Stormont’s Executive has announced that, depending on the rate of infection, caravan parks, camping sites and self-catering tourist accommodation would be able to reopen on Friday.
Hotels and other tourist accommodation would be able to reopen from July 3 along with restaurants, cafes and coffee shops.
Pubs and bars can also open from July 3 for the provision of food, and also trade in their beer gardens on a table service basis.
The guidance – entitled Working Safely During Covid-19 in the Visitor Economy – is aimed at business owners, operators and workers in hotels and other tourist accommodation.
The minister also announced that there will be a new industry standard and consumer mark developed by national tourist boards across the UK.
Northern Ireland Hotels Federation chief executive Janice Gault said: “The industry has gone through a period of considerable change and is keen to return to trading with the appropriate safety measures in place, and in a manner which is Covid-19 compliant.
“It is important that we mitigate the risk of spreading the virus.” Hospitality Ulster chief executive Colin Neill said the guidance aided preparations for reopening.
“The entire industry has been dealt the biggest body blow for a generation and for many business owners it has swept the feet from under them,” he said.
“We are now hopefully emerging from that extremely difficult period.”