NFPA Journal - September/October 2017 - 54

The Science of

Flame Jetting 101
FROM ITS RESEARCH into flame jetting,
which it began in 2010, the Fire Research
Laboratory at the Bureau of Alcohol,
Tobacco, Firearms and Explosives has
determined that, while multiple variables
can affect whether a flame jet will occur
and how long it will be, certain common
denominators exist:
1. Almost any necked portable flammable
liquid container with a flammable liquid-
those with flash points less than 100 degrees F, such as gasoline-can jet. Containers with large openings, such as buckets,
cannot jet. In addition to gasoline, common
flammable liquids include methanol, ethanol, acetone, and liquor above 150 proof.
2. Flame jetting is typically observed when
the container is being tilted and vapors are
pouring from the mouth of the container. This allows air to be entrained in the
container headspace, diluting the rich fuel
vapors in the headspace to within their
flammable limits.
3. If the container has a nozzle installed when combustion occurs,
flames can travel back into
the container. The nozzle restricts expanding gases from
venting, resulting in rupture
along the container seam.
Flames are expelled where

of thermal or pressure damage to the
container. The length of the flame jet was
dependent on several variables, including
the total quantity of liquid, the mixture
ratio, and the percentage that the gasoline was "weathered," or evaporated.
On this point, flame jetting was only
observed with weathered gasoline-25
percent weathered gasoline by weight
was evaluated. No flame jetting was
documented when "fresh" gasoline
was poured from the container. Fresh
gasoline releases vapors more readily
than weathered gasoline at the same
temperature. Consequently, it is hypothesized that even when air is entrained

54 | NFPA JOURNAL * S E P T E M B E R / O C T O B E R 2 0 1 7

the container fails, injuring the person
holding the container.
4. If no nozzle is installed when flame jetting occurs, typically the person pouring the
container is uninjured and injuries will occur
to victims located opposite the container.
Frequently there is no thermal or pressure
damage to the container.
5. The longest flame jets occur when a
container is about one-third full of liquid,
regardless of the container's capacity. This
allows for sufficient vapors to accumulate
in the head space of the container and for
sufficient flammable liquid to be expelled
when jetting occurs.
6. In cases involving gasoline jetting, older
(weathered) gasoline that has undergone
evaporation is more prone to jetting as it
releases vapors more slowly than fresh
gasoline. This means it can support flame
propagation inside the portable flammable liquid container if an ignition source is
present and combustion occurs.
7. Flame arrestors (pictured) are
highly effective in preventing flame
jetting-and typically cost about
50 cents. In ATF testing, no flame
jetting was observed in portable
flammable liquid containers
equipped with flame arrestors.

into the container headspace while
pouring, fresh gasoline releases flammable vapors readily enough that the
headspace never drops below the upper
flammable limit and therefore does not
support flame propagation within the
container. Weathered gasoline, by comparison, is slower to release vapors and
can support flame propagation inside
the container, leading to flame jetting.
The ATF FRL testing results
supported the argument that the
daughter's death in the Michigan case
was likely a tragic accident. The father's
inability to explain the flame-jetting
event was consistent with the rapid

development and unpredictable nature
of the flame-jetting phenomenon. The
prosecutor dropped the murder charges
and the father pled guilty to misdemeanor child endangerment charges.
The self-evident nature of the ATF FRL
forensic tests prevented a likely innocent person from being charged for a
crime he did not commit.
As a result of this case and others, as
well as continued incidents in educational settings-including one in May
at a Texas pre-school, where a dozen
three-year-olds suffered flame-jetting
burns-the hazard of flame jetting is
receiving wider attention. Earlier this
year, a bill was introduced in Congress
designed to reduce the number of
people injured in these incidents. The
Portable Fuel Container Safety Act of
2017, currently in committee, would
require flame arrestors on portable
flammable liquid containers.
Flame arrestors have been shown
to be highly effective at preventing
flame jetting. Liquid from the portable flammable liquid container can be
poured through the arrestor's screen,
but if an ignition source is present and
combustion occurs, the device prevents
the flame front from traveling through
the mouth of the container and into
the headspace above the liquid. The
ATF FRL conducted seven tests with a
flame mitigation screen in the mouth
of the same portable flammable
liquid containers used in the previous
flame-jetting tests. The flame-arrestor
screens prevented flame jetting in all
seven tests. Flames never propagated
beyond the location of the screen.
Flame mitigation devices were successfully utilized for decades in mining
lamps, and more recently they've been
used in mufflers, high-proof liquor
bottles, and in some commercial
flammable liquid containers. Despite
being highly effective and relatively
inexpensive, the vast majority of consumer-grade portable flammable liquid
containers are not currently equipped
with the device, which the bill in Congress aims to reverse.
ADAM ST. JOHN, P.E., is a licensed fire
protection engineer at the ATF's Fire Research
Laboratory.

ATF FIRE RESEARCH LABORATORY

FL A ME JETTING

Table of Contents for the Digital Edition of NFPA Journal - September/October 2017