Enforcement Policy for the replacement of iron gas mains 2006 - 2013 - December 2005
- In September 2001 HSE published its enforcement policy for the
replacement of iron gas mains for the period 2002 - 2007. This followed
a high level of societal concern about the potential consequences of gas
mains failure. At that time records showed there were about 91 000 km of
iron mains within 30m of property ('at risk') which may be a risk to
- HSE considered it realistic and practical for Transco plc, who owned
and operated all the gas distribution networks, to speed up its rate of
mains replacement over the 5 year from April 2002 - March 2007 so that
it was in a position to complete the replacement of all the remaining
'at risk' iron mains within 30 years.
- Given the uncertainty about this issue, HSE undertook to review the
policy before the end of the first five years so that an agreed
programme could be confirmed for the following period. HSE published its
report 'Review of the Health and Safety Executive's enforcement policy
for the replacement of iron gas mains' in September 2005.
- This policy updates the 2002 - 2007 policy taking account of the
recent review, the structural changes in the gas distribution industry
since 2001 and new legislation concerning approved mains replacement
- There are a small number of local networks using iron mains. These are
not included in this policy and are being dealt with on a case-by-case
basis, for example via their GSMR safety cases.
- The Health and Safety at Work etc. Act 1974 (HSWA), section 3(1),
requires gas conveyors to conduct their undertakings to ensure, so far
as is reasonably practicable, that persons not in their employment are
not exposed to risks to their health and safety. In making a judgment on
what is 'reasonably practicable' the courts will take into account
standards which have been achieved in the past.
- The Pipelines Safety Regulations 1996 (PSR), regulation13, requires
the operator to ensure that a pipeline is maintained in an efficient
state, in efficient working order and in good repair. The duty is
absolute with a limited defence if a third party damages the pipeline.
In respect of iron gas mains, there is no feasible alternative to
maintaining the network in a safe condition other than to decommission
it and replace it with a more suitable material.
- In 2003 PSR was amended, enacting regulation 13A, allowing operators
of iron gas mains to submit a mains replacement programme to HSE.
Providing it is suitable and sufficient, HSE must approve it. HSE can
also prepare and approve a programme where no suitable one exists.
Regulation 13A legally underpins the replacement programmes and gives
operators of iron gas mains a defence if a pipeline fails provided they
were following the approved programme and did not know and could not
have reasonably have been expected to know, before failure, that there
was a risk of the pipeline failing. HSE approved the first replacement
programme for Transco plc for the period April 2004 - March 2005.
- The Gas Safety (Management) Regulations 1996 [GSMR] require gas
conveyors to operate their networks in accordance with an accepted
safety case. Mains replacement programmes form part of the safety case.
- In June 2005 Transco plc sold four of their eight gas distribution
networks [DNs] - Scotland, North of England, Wales & West and South
of England. The four new distribution network operators now have
approved mains replacement programmes.
30 year replacement programmes
- Annex 1, Table 1 shows the baseline replacement programme HSE set
Transco plc for the five-year period 1 April 2002 - to 31 March 2007.
The profile describes the ramp-up rate required over the first five
years to a plateau to enable decommissioning of all iron mains within
30m of property within a maximum of 30 years.
- In May 2003 Transco proposed changes to the way they prioritised
replacement of mains. HSE accepted this approach provided an equivalent
amount of risk was removed from the network. This meant that an extra
10% of mains per annum would have to be decommissioned, resulting in a
'baseline +10%' replacement profile as shown in Annex 1, Table 2.
- At the start of the programme, records showed there were some 91 000
kms of iron mains requiring decommissioning. However, a review of
records in March 2004 identified there were some 101 000 km of mains at
risk at the start of the programme in 2002, ~ 10% above initial
- The outcome of these two factors gives a new replacement profile shown
in Annex 1, Table 3.
Replacement performance since April 2002
- Over the first three years of the 2002 - 2007 5-year programme, the
accelerated replacement targets were substantially met as shown below.
30/30 iron mains to be decommissioned (km)
Jan 2002 - March 2003*
April 2003 - March 2004
April 2004 - March 2005
Baseline + 10% target
* The period January 2002 - March 2003 was a 15-month period following
publication of HSE's enforcement policy and included 1411 km of medium
pressure ductile iron mains [MPDI] which completed removal of 2800km of MPDI
to comply with an earlier Improvement Notice.
- This replacement confirmed HSE's opinion that it was realistic and
practicable to accelerate the replacement rate.
HSE's iron mains replacement policy
- Whilst the first three years have been successful in removing risk,
there remains uncertainty about the safety of an aging network. At April
2005 there were still ~ 93 000 km of iron gas mains within 30m of
property, resulting in ~ 11 500 fractures and corrosion failures and ~
940 gas in buildings events in the previous year. In the year January -
December 2004, there were two major gas explosions in domestic
properties resulting from leaks from pipes supplying the premises, one
from a gas main and the second from a steel service pipe. Fortunately
there were no fatalities. HSE remains committed to ensuring risks to the
public from gas mains failures are minimised and that iron gas mains
should be decommissioned.
- HSE considers it realistic and practicable for the DN operators to
continue to speed up the rates of mains replacement to a minimum rate of
3500 km/annum by 2007. Replacements rates should then continue at least
at this level so that the remaining population of at risk mains can be
replaced at the latest by March 2032.
- Each of the existing eight DNs will be expected to contribute to the
annual national replacement targets. The DNs will be required to prepare
annual mains replacement programmes for approval by HSE in accordance
with PSR regulation 13A. These arrangements will form part of their
- HSE will encourage proposals from DNs for increasing replacement rates
and improving the effectiveness of the 30-year programme.
- HSE intends to review the policy before the end of 2013 so that an
agreed programme can be confirmed for the following period.
Medium pressure ductile iron [MPDI] mains
- HSE required Transco to decommission all MPDI mains within 30m of
property by 30 April 2003, resulting in excess of 2800 km being
- Serious concerns remain about the integrity of MPDI mains and any
additional lengths which are found or become 'at risk' must be replaced
as soon as reasonably practicable and in any case within 12 months.
Prioritising mains replacement
- DN operators should set out their policy and procedures in their GSMR
safety case for implementing and managing their mains replacement
programme to meet the objectives of this policy. These arrangements
should include how the annual replacement programme is prioritised. The
criteria for establishing the replacement programme should meet the
requirements in HSE's GSMR safety case assessment manual.
- 25 HSE will monitor the performance of DN operators in meeting
replacement targets in accordance with HSE document 'Monitoring and
reporting of the Distribution Mains Replacement Programme 2006 - 2013'.
This updates an earlier document covering the period 2002 - 2007 and
covers Ofgem's next price control review period 2007 - 2013.
ANNEX 1 - Iron mains requiring decommissioning within 30m of buildings:
Table 1 - 30/30 Baseline profile - 91 000 km
Table 2 - Plan (April 2005) based on replacing 91 000 km
Table 3 - Potential profiles for replacing 101 800 km