A major investigation has been launched after it emerged that respiratory masks destined for medical staff in Northern Ireland may not have been tested properly.
The Public Health Agency last night confirmed that an audit review of fit-testing for respiratory masks is ongoing within the Health and Social Care system.
"This is being done on a precautionary basis," the PHA said in a statement.
"It has emerged that one independent contractor, which conducted fit-testing of masks during the pandemic, had inadvertently applied on some occasions a fit-testing setting not normally used in Northern Ireland.
"This should have been readjusted to the UK fit-testing requirements.
"We are advised that any risk to staff is likely to be low.
"The HSC system is now carrying out a validation and audit exercise of all fit-tests conducted by this independent contractor."
The PHA has been asked by the Department of Health to undertake a serious adverse incident review.
This is defined as any event or circumstance that led or could have led to serious unintended or unexpected harm, loss or damage to patients.
They must be carried out after an incident resulting in serious harm, or an unexpected or unexplained death, for example.
Incidents may include infection outbreaks in a hospital or the failure of equipment.
"Additional measures across the HSC will be put in place to review and monitor fit-testing outcomes moving forward," the PHA said.
"Staff impacted will be informed and offered support. Fit-testing will be carried out under the correct NI setting.
"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. Further information will be made public following the conclusion of the audit."
Health union Unison had been advised last Thursday by health trusts of a regional alert in relation to PPE fit-testing carried out for trusts by an external company.
It said it was told that some staff may have received a positive fit-test when, in actual fact, under HSE standards this may not have been the case.
Unison regional secretary Patricia McKeown said last night her "main concern is the extent to which our members have been exposed and what liability lies with employers and the department".
"I think there are more issues here than the calibration of machines. We raised concerns about nature of the masks, and the instruction at least one company gave to tie knots in them to make fit," she said.
"There was a major issue about masks being generally made to fit a larger male face, rather than a smaller female face - and the majority of staff are women.
"We will certainly be giving evidence to any inquiry being carried out."