Sean Gibson, head of estate management at the Western Health Trust, said the hospital is using between 800 and 900 litres of oxygen a minute.
That is almost three times normal levels.
“I am concerned there isn’t enough oxygen to treat patients – that’s the biggest concern,” he told BBC News NI.
“If we experience the growth in numbers that we have, then we may not have enough oxygen to treat them.
“We may have to ration oxygen – it’s that serious.”
The hospital has developed a green, amber and red alert system to monitor the oxygen levels in a specially converted tank from Harland and Wolff shipyard in Belfast.
At present the levels are between green and amber – but just last week they were edging towards red, warned Mr Gibson.
“If things continue as they are then we will be in the red very, very quickly which is a very, very serious situation,” he added.
“This plant has never seen this type of oxygen usage. It’s designed to deliver but we don’t really know until we see it happening.
He said he felt “very responsible that I can deliver the oxygen they require to get well and take the pressure off the hospital”.
“Patients, when they come into the hospital they take for granted there will be oxygen available to them,” he said.
“Well, that’s no longer the case.
“We have to remember all the other types of patients that are here – cardiology, maternity – they all need oxygen at some stage.
“But it’s all being very focussed on our Covid patients – they can take up to 80 litres a minute – typically 50 litres a minute per patient.
“If you do the maths that’s a lot of oxygen.”
Mr Gibson said they did not want to be in a position where available oxygen levels meant teams would have to choose between patients who received it.
The worries about oxygen supplies are echoed throughout the sprawling hospital site.
On ward 26 – one of three dedicated Covid recovery units – nurse Mairead Meenan also expressed concerns.
The 51 year old from Creggan in Derry worked her way through the first wave of the pandemic but said it is now “completely different”.
“We are on our knees at work,” she said.
“People are coming in and they are so, so sick – it’s completely different from the last time, it’s scary watching them.”
She added: “On our ward at the minute we don’t have anybody who is under eight litres of oxygen.
“That is a high volume of oxygen. So all this oxygen is being used at the one time – we have to spread it out, we have to be careful. It’s just crazy.
“The oxygen is so important for the patients – they could become hypoxic where there is not enough going round their body.
“They are becoming so sick.
“So, we need to deliver it to them.”
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