and local authorities with their own gas mains that medium pressure
ductile iron (MPDI) pipes need to be replaced.
agreed accelerated programme of replacement of all MPDI gas mains
located within 30 metres of buildings. This work is due for
completion by the end of 2002.
The risk of failure of MPDI mains located close to buildings is such
that they should be replaced on all networks as soon as reasonably
practicable. As a result HSE is to begin a programme of work to
ensure non-Transco MPDI networks are also replaced as soon as
HSE has recently been notified of a small number of sites where such
networks may be in place and are contacting the owners of these
premises. HSE is also contacting the owners of other sites such as
hospitals, universities, prisons, Ministry of Defence premises as
well as some industrial and commercial premises to eliminate any
other potential problem areas.
Dan Mitchell, head of land division, HSE Hazardous Installations
'Presently we don't know how many of these networks exist. Although
Transco has brought a number to our attention, there may be many
more. Occupiers of large sites and local authorities need to
establish who own the pipes, determine what material they are made of
and, where appropriate, implement a suitable programme of
'The problem with ductile iron is that it can fail unpredictably. In
view of this and the difficulties with accurately assessing its
condition, mains close to property need to be replaced as soon as
reasonably practicable. As Transco's programme is drawing to a close,
HSE is now turning its attention to other organisations who may own
'This is an important issue and inspectors will be taking a firm
enforcement line to ensure occupiers take the necessary action
While HSE is currently focusing on MPDI networks, occupiers and local
authorities should be aware that there is also an aging population of
cast iron and low pressure ductile iron networks which should be
considered for replacement.
1. Cast iron mains can fail unpredictably particularly through
fracture if exposed to excessive loading, such as heavy traffic or
ground movement. Ductile iron pipe was introduced in the 1970s in
response to problems with cast iron. It has greater strength and
flexibility compared with cast iron. It was later found, however,
that ductile iron could fail unpredictably through corrosion. When
this happens, there is a risk that the gas will track into adjacent
properties, where it may subsequently be ignited. Ductile and cast
iron have now been superseded by polyethylene for all low and medium
2. Transco has already replaced all MP cast iron mains below 12'
diameter within 20 metres of property.
3. 'Medium pressure' means a pressure above 75 millibar.
4. An Improvement Notice was served on Transco in September 2000 to
confirm an agreement reached that all 'at risk' MPDI mains should be
replaced by the end of 2002, a total length of 2,300 km.
5. An Improvement Notice is a statutory notice requiring specified
improvements to be made within an agreed time scale. A failure to
comply is a prosecutable offence under the Health and Safety at Work
etc. Act 1974 (the HSW Act).
6. Recipients have the right to appeal against an Improvement Notice
under Section 24(2) of the HSW Act, which states: 'A person on whom a
notice is served may within such period from the date of its service
as may be prescribed appeal to an Employment Tribunal; and on such an
appeal the tribunal may either cancel or affirm the notice and, if it
affirms it, may do so either in its original form or with such
modifications as the tribunal may in the circumstances think fit.'