HSL Report

HSL Report

Public information on risks from passing LNG ships in the Milford Haven estuary produced by the Health and Safety Laboratory (“HSL”).


Due to the depletion of North Sea oil and gas reserves, liquefied natural gas (LNG) imports are needed to ensure the UK is better able to meet peaks in demand and have gas available when required. This need is recognised in Government policy, for example the Overarching National Policy Statement for Energy. Two of the UK’s LNG terminals are situated on the Milford Haven estuary. LNG is transported to Milford Haven in specifically designed and purpose-built ships commonly referred to as LNG carriers. The design of LNG carriers has developed since LNG was first transported commercially in the 1960s and during that 50 year period, no accidents have occurred worldwide which have resulted in any harmful release of LNG.   Notwithstanding that safety record, the purpose of this note is to provide information to the public about such risks as originate from LNG carriers in the Milford Haven estuary.

Liquefied Natural Gas (LNG)

Liquefied Natural Gas, LNG, is a natural gas (the same gas supplied to homes and offices) consisting of primarily methane in liquid form having been cooled down to very low temperatures (approximately -160ºC).

In liquid form, the volume occupied by a given amount of natural gas is considerably smaller than that occupied by the same amount in the form of a gas. This reduction in volume enables cost-efficient transport of LNG over long distances, such as those required for the import of LNG into the facilities at Milford Haven.

Hazards associated with LNG usually only arise when it is released into the open and expands to form natural gas. In the highly unlikely event of accidental release and subsequent ignition, fire and (if released in a confined area) possible explosion could result. LNG is not toxic but releases of LNG can also pose asphyxiation hazards in the area immediately around the release due to oxygen displacement caused by the natural gas vapours and freeze burn hazards due to the low temperature.

Assessing Risks to the Public

Prior to the construction of the LNG terminals in Milford Haven, Milford Haven Port Authority, the LNG terminal operators and the UK Health and Safety Executive (HSE) undertook extensive and detailed work to assess the potential risks to the public and to implement measures to reduce the risks to the accepted standard of “as low as reasonably practicable (“ALARP”).

Milford Haven Port Authority used the results of the work done to assess the risks and to help define strict procedures for when LNG carriers are in the estuary, so as to effectively eliminate risk of LNG releases from collisions and grounding.  Measures such as (a) creating exclusion zones around the vessels requiring greater room to manoeuvre and deploying guard vessels to ensure compliance, (b) ensuring other services such as tugs, line-boats and berthing gangs are available and deployed in good time, (c) requiring two pilots for each LNG carrier of whom (i) the senior pilot must be authorised to handle any vessel (which qualification takes up to 6 years training (including annual simulator exercises) and experience to obtain) and (ii) the second pilot is currently also unrestricted, providing a check to the charge pilot and preventing distractions and (d) imposing speed restrictions within the Haven, were all implemented as a result.

HSE’s assessments as part of the planning process helped to provide advice on whether to grant consent for the LNG terminals and for any subsequent land development adjacent to the terminals. HSE uses a ‘3 Zone Map’ around a site to provide its advice . HSE uses a ‘cautious best estimate’ approach so that their advice is precautionary – the actual risk that exists should always be smaller than predicted in their assessments. HSE’s assessments are also used to set Public Information Zones around the terminals. The public within this area are provided with the necessary safety instructions about the steps, if any, to be taken in the event of an emergency.  

LNG transport risk assessment 

The work undertaken by Milford Haven Port Authority and the terminal operators is complex and highly technical, Welsh Government instructed the Health and Safety Laboratory (HSL) to produce an independent report recently to explain in a manner more understandable to the general public the risks associated with the transportation of LNG through the estuary. The HSL Report has been based on a similar methodology to that used by HSE for land-based risks in the planning process and a copy can be accessed here. The results of HSL’s work are summarised below and conclude that there is a negligible risk of harm to local residents.

The methodology uses a number of assumptions. Risks from LNG carriers delivering to each terminal have been calculated considering the maximum projected number of LNG carriers in the estuary over a year of operation.

The length of time for which an LNG carrier is present anywhere within the jurisdiction of the Milford Haven Port Authority depends on that LNG carrier’s course and speed.  Both are determined by harbour procedures adopted by the Port Authority to mitigate risk and facilitate safe operations The Port Authority’s data derived from these procedures has been used to calculate the length of time and relative position of carriers transiting to and from the LNG terminals. 

Whilst globally there have been more than 80,000 LNG carrier voyages covering more than 100 million miles over the last 40 years or so, the operating experience of the Port Authority for other vessels of a comparable size is even more extensive and helps to inform the Port Authority’s safe working practices for all vessels.  No LNG carrier accidents have occurred anywhere in the world which have resulted in any release of LNG sufficient to cause harm to the public. The likelihood of LNG releases that has been used in the HSL work has been assessed on the basis that it is much more likely than it would be in reality and is benchmarked against the operating experience so far.

In common with HSE’s methodologies for land use planning advice, HSL assessed the risk to a hypothetical person (both indoors and outdoors) of receiving a ‘dangerous dose’ or worse. The “dangerous dose” criterion is based on the level of exposure that would cause:-

  • almost all exposed individuals in the area severe distress;
  • a substantial number of the exposed population to require medical attention;
  • some individuals to be seriously injured and require prolonged treatment; and,
  • a small proportion of highly susceptible people to be possibly killed.

HSL conclude that the risk of anyone receiving a dangerous dose is negligible, and that even with that negligible risk of a flash fire extending to the shore, the proportion of fatalities where people are outdoors would be very small indeed, namely some 1%, with the figure becoming a small proportion of that number for those indoors. In reality and depending on its location, were an incident to occur then members of the public within the Public Information Zones would be given information by the terminal operators as to the steps they should take to minimise harm and similarly, were there to be an emergency in the Haven, MHPA would activate its Port Contingency Plan to inform all users, including the public, about the steps they should take on the water to do likewise. 

LNG transport risk

The likelihood of a release and the hazardous events that can follow has been shown to be negligible by HSL’s work.  The risk of an individual experiencing a dangerous dose is also negligible.  The risks are well below the levels used by HSE to present contours for the three zone maps used to give planning advice.  In all cases the individual risk levels are at least an order of magnitude less than the lowest risk level applied by the HSE for the purpose of land use planning.  Consequently, HSL concluded the risk level associated with the shipment of LNG in the Haven may be regarded as negligible.

Download the Health and Safety Laboratory Report