(118a) QRA Method for Liquified Natural Gas (LNG) Filling Stations

Summary

This
paper describes a method to calculate risks generated by liquefied
natural gas (LNG) filling stations for road trucks. An increasing
number of these stations is operational in the Netherlands and they
require activities such as transfer, storage, saturation and supply
of LNG. Under the Dutch legislative context, facilities that handle
or store large amounts of hazardous substances must carry out a
quantitative risk analysis (QRA) for land-use planning purposes. The
outcomes of the QRA determine the kinds of activities that are
tolerable in the surroundings of the facility. The current method
defines which release scenarios and frequencies must be used and how
consequences of release scenarios must be calculated. The project was
carried out by RIVM (Dutch National Institute for Public Health and
the Environment) and DCMR Environmental Protection Agency and was
supervised by an advisory committee. Designers of LNG filling
stations supplied technical information.

Background

In
The Netherlands, legislation is in place that obliges facilities that
handle or store large amounts of hazardous substances to perform a
quantitative risk analysis for land-use planning purposesⁱ.
Off-site risk is expressed with two indicators: individual risk (IR)
and societal risk (SR). IR is used to determine a zone where the
presence of structures such as houses and schools is undesirable or
unacceptable. SR is used to determine whether the remaining risk
level, related to the number of people, present in the vicinity of
the facility,, is tolerable. A method (hereafter ‘QRA manual’)
is in place that prescribes how this risk analysis should be carried
outⁱⁱ.
Currently, the QRA manual deals with large chemical industries,
pesticide storages and LPG filling stations among others. The method
might have to be extended with LNG filling stations.

The
use of QRA results for public decision making for current and future
land use requires a method that is transparent and robust. The
stakeholders must be able to verify the method and therefore only
generally accessible data can be used for the derivation of release
frequencies and for consequence calculations. The outcomes of the QRA
should not depend on subjective choices of risk analysts or
differences in software models. Therefore, the method to carry out a
QRA is prescribed by legislation, including the prescribed use of the
software tool Safeti-NL™ from DNV. In order to achieve
coherence, the QRA method for LNG filling stations should follow the
method for general chemical industries and LPG filling stationsⁱⁱⁱ
where possible.

Scenario
identification and frequency analysis

A
reference LNG filling station was defined to develop relevant
scenarios and frequencies. The various engineering choices for
setting up a LNG filling station were taken into consideration when
possible. An example of such an engineering choice is the transfer of
LNG by using the pump on the truck or by building up a higher
pressure in the truck vessel. Another choice is the pressure used for
LNG saturation (9 and/or 18 bar) depending on the motor system of the
truck using the LNG as fuel. Safety measures were identified and
rewarded when possible. For example, using a composite material for
the supply hose reduces the release frequency with a factor 10.

The
activities that take place at LNG filling stations and the equipment
that is used for these activities are listed in Table .
Most activities are considered relevant for the risk assessment.
Systems only containing gaseous (and not liquefied) natural gas do
not have to be included in the QRA.

Table Relevance of various activities for the risk outside the facility

Table gives
an overview of the equipment types for which scenarios and
frequencies have been either investigated or copied from the existing
framework. In the extended paper, all releases scenarios and
corresponding frequencies will be reported. Also a number of
conditions for which the described method cannot be directly
considered valid will be listed.

Table Source of scenario identification and frequency estimation

Consequence
calculation

The
consequences associated with a release are calculated with Safeti-NL™
from DNV. The validation of the release models for LNG was supplied
by DNV^iv.
The largest consequences relate to flash fire and BLEVE of the truck.
The amount of LNG that is released in case of a hose rupture was
investigated in detail by RIVM.

Outcomes

For
a typical filling station with an annual throughput of 5000 m³,
the safety distance to be used for land-use planning can vary between
40 and 135 meter. The lower value applies to the situation of no
external impact for the truck and the upper value applies to the
situation where a ‘hot BLEVE’ of the truck is possible.
The dominant events and corresponding consequence distances will be
discussed in detail in the full paper. When compared to a typical LPG
filling station with (with a comparable annual throughput of 1.000
m3) the safety distances for an LNG station turn out to be slightly
larger.

Conclusions

A
method is described to calculate the off-site risk resulting from
activities at LNG filling stations. The specific design of the LNG is
taken into account and therefore may affect the safety distances.
Generally speaking the safety distances for LNG filling stations are
slightly larger then for LPG filling stations. This is due to the
higher turnover of a LNG station which results in a higher number of
risk determining LNG transfers from the truck to the storage vessel.