NFPA Journal - Winter 2024 - 55

U.S. Department of Transportation
(DOT), Transport Canada, and the
Secretariat of Infrastructure, Communications,
and Transportation of Mexico,
the ERG helps emergency personnel
quickly identify the hazards of the
materials involved in an incident and
implement protective measures.
The guide contains emergency recommendations
tailored to products that
share certain physical and chemical
properties. The emergency actions in the
ERG are updated periodically to account
for changes in the transport of dangerous
goods landscape, such as changes in commodity
flows, improvements in means of
containment that reduce the likelihood
of a release or failure, and the generation
of new scientific knowledge that may
change the assessment that applies for a
particular substance.
The Emergency Response Guidebook
typically classifies substances with similar
physical and chemical properties
together. Liquefied natural gas, usually
consisting primarily of methane in a
mixture with small amounts of other
hydrocarbons, is currently assigned
to Guide 115 in the ERG, along with
liquefied petroleum gas. Therefore, the
emergency actions for both LNG and
LPG are currently identical. However,
there are differences in the way the
substances are transported that may
alter their hazard profile if an incident
were to occur.
Liquefied petroleum gas is liquefied
under pressure and transported
in single-walled containers capable
of sustaining these pressures during
transport. By contrast, LNG is liquefied
under extremely low temperatures.
The product is kept cold using double-walled,
insulated tanks that are not
suited for the higher pressures required
for the transportation of LPG. Other
key differences between these two substances
include the following:
LNG forms pools of liquid product
when released, whereas LPG generally
does not, thus their dispersion profiles
following a release are different.
LNG is odorless upon release,
whereas LPG is not.
LNG has greater volume reduction
when liquefied-600x, compared to
270x for LPG.
Both substances initially release as
dense clouds close to the ground; however,
LNG rises after warming.
LNG experiences rapid phase transition
(RPT), which is the instantaneous
conversion of cryogenic liquid (e.g.,
refrigerated liquefied gas) to vapor
when it comes in contact with water,
which may result in an explosion.
LPG poses a greater risk of a boiling
liquid expanding vapor explosion
(BLEVE) and has a more rapid flame
spread than LNG when ignited.
LNG has a substantially higher heat flux
factor (3 to 5x) than other commonly
transported hydrocarbons, thereby
increasing thermal impact distances.
The " tank within a tank " design (i.e.,
double-walled tank) utilized for LNG
transport results in added protection
for the inner container due to the
annular space. LPG containers are generally
single-walled and therefore do
not have this added protection.
Although it is not commonly encountered
by emergency responders, the
risk of metal embrittlement of an LNG
outer tank shell exists, whereas it does
not for LPG.
These differences in the properties of
LNG and LPG have raised questions as
to whether it is appropriate for them to
be covered in the same section of the
Emergency Response Guidebook.
The FPRF study found that in order
to establish comprehensive response
guidance, the use of the ERG should
be complemented by the application
and use of a risk-based response and
analysis process, outlined in NFPA
470, Hazardous Materials/Weapons of
Mass Destruction (WMD) Standard for
Responders, to include the facts, science,
and circumstances of the incident.
Recognizing that LNG is transported
as a gas liquefied by cooling at cryogenic
temperatures, and that LPG is
transported as a gas liquefied under
pressure, the hazard profiles of LNG
during an incident may look vastly different
than those for LPG. As a result,
the research team identified key risk-related
scenarios for LNG transport that
should be considered when evaluating
the adequacy of the response guidance
that currently exists in the ERG.
The four key risk-related scenarios
included cryogenic behavior and effects,
where extremely low temperatures can
cause severe damage upon contact; fire
scenarios, including pool fires, jet fires,
vapor cloud fires, and boiling liquid
expanding vapor explosions; vapor
cloud explosions, which are particularly
hazardous in confined spaces; and rapid
phase transition, where LNG vaporizes
violently upon contact with water, causing
a physical explosion.
The analysis resulted in a number of
recommended amendments to various
sections of Guide 115 to ensure that
appropriate considerations for LNG are
included. Each recommended amendment
was discussed by Transport
Canada and the other partner organizations
(the U.S. DOT, the SICT of Mexico,
and the CIQUIME of Argentina) who
develop the ERG.
Ultimately, the ERG Guide 115 was
found to accurately capture the hazards
associated with LNG and related
flammable cryogens and was found
to be consistent with the ERG structure
of classifying refrigerated liquids
into flammable gases, inert gases, and
oxidizing gases. The potential need
to develop a separate ERG for LNG
was deemed unnecessary at this time.
However, incorporation of the modified
language proposals for ERG Guide 115
made the existing guidance more inclusive
of LNG.
To read " Validation of Recommended
Emergency Actions for Liquefied Natural
Gas (LNG) in the Emergency Response
Guidebook (ERG), " the full report published
by the Fire Protection Research
Foundation, please visit nfpa.org/foundation
and click on " projects and reports. "
VICTORIA HUTCHISON is senior research
project manager for the Fire Protection
Research Foundation.
NFPA .ORG/JOURNAL * NFPA JOURNAL | 55
https://www.nfpa.org/en/codes-and-standards/nfpa-470-standard-development/470 https://www.nfpa.org/en/codes-and-standards/nfpa-470-standard-development/470 https://www.nfpa.org/en/codes-and-standards/nfpa-470-standard-development/470 http://www.nfpa.org/foundation https://www.nfpa.org/en/codes-and-standards/nfpa-470-standard-development/470 http://www.nfpa.org/foundation http://nfpa.org/journal
NFPA Journal - Winter 2024

Table of Contents for the Digital Edition of NFPA Journal - Winter 2024
