Patients were evacuated from medical buildings near the Buncefield Terminal yesterday following a gas leak.
Private medical clinic OSD Healthcare, on Boundary Way in Hemel Hempstead, was closed and cleared from about 3.30pm.
The site is less than one mile from the Buncefield fuel depot - where in 2005 a tank overflowed and caught alight, causing the UK's largest peacetime blaze.
Cadent Gas, which operate and maintain the gas distribution network in that area, said a service pipe had been damaged by a third party at about 1pm.
A spokesperson said it is unlikely to be a "large scale leak".
However, a statement on OSD Healthcare's website read: "Please note that a major gas leak has been reported in the local area.
"As a result of this, we have been advised to evacuate and close the clinic."
It reopened later on September 4.
In 2017, the BBC reported that the site would once again be used to store fuel but conceded there had been "no official word" from the British Pipeline Agency.
BP store jet fuel at a neighbouring tanker, the Hemel Hempstead Terminal. Ground fuels like petrol and diesel were also kept there in 2014.
Cadent Gas stressed that suspected gas leaks should be reported on 0800 111 999.
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