Chemical Engineering April 2020 - 54

Environmental Manager
Detection Systems for
Reducing the Risk of Hydrogen Fires
Today's detection equipment can provide early sensing of H2 gas and flames, provide
alarm information to a fire- and gas-safety system controller to initiate mitigating
measures, and integrate with process control to further minimize H2 fire risk
Michael J. Hosch and
Aaron Paterson
Det-Tronics
H
ydrogen is the most flammable
element on earth
[1]. However, this colorless,
odorless and tasteless
substance rarely exists in its pure
form. Instead, it normally combines
with other elements, in water molecules,
for example, or in industrial
compounds. However, H2 is widely
used in the chemical process industries
(CPI, Figure 1). For example, in
the chemical industry, it is an important
component in the production
of polymers and ammonia for fertilizers.
In petroleum refining, it is used
in the reforming process for producing
high-grade gasoline, as well as
in removing sulfur compounds from
petroleum so they will not poison vehicle
catalytic converters [2].
According to the U.S. Dept. of
Energy's Office of Energy Efficiency
& Renewable Energy (www.energy.
gov/eere), 10 million metric tons of
H2 are produced in the U.S. annually
[3]. While playing an indispensable
role in many processes, H2 also
poses a unique and potentially significant
threat to chemical processing
facilities. The dangers to personnel
and property, however, can
be minimized by choosing the right
equipment to detect and respond to
hydrogen-related hazards.
Challenges with H2
The challenge with using H2 in CPI
plants and other industrial settings
is that this nontoxic and seemingly
harmless gas has
highly
54
reactive
and explosive properties. In fact, the
National Fire Protection Association
FIGURE 1. Hydrogen is widely used throughout the chemical process industries
(NFPA; Quincy, Mass.; www.nfpa.org)
- the main fire codes and standards
organization in the U.S. - gives H2
its highest rating of " 4 " on the flammability
scale (Figure 2), because H2
is flammable when mixed with other
elements, even in small amounts with
ordinary air [4].
In addition, it only takes a small
amount of energy to ignite H2. The
gas can even self-ignite without energy
from an external source when it
is leaking from a pipe at high pressure.
Making matters more challenging
for plant personnel and unlike a hydrocarbon
flame, a H2 flame cannot
be easily detected by human senses
(Figure 3). Workers approaching a
H2 flame may not see it, even up
close. Instead, they may see a shimmering,
mirage-like area or possibly
sparks, which are actually dust particles
burning briefly in the flame.
Adding to the danger, personnel
approaching a H2 flame will not
feel intense heat. This is because
H2 flames typically emit less of the
infrared (IR)
radiation that causes
humans to sense heat when near a
flame than hydrocarbon fires.
With little or nothing to see and a
small amount of radiant heat to be
felt, human senses may not warn
people to stop as they approach a
H2 flame, potentially allowing them
to unknowingly walk right into it.
First line of defense
For the reasons just mentioned,
chemical plants that use H2 need
fire and gas (F&G) safety systems
with flame and gas-leak detection
technologies in order to minimize
fire-related risks to personnel and
processes. The first line of defense
against H2-related dangers is gas
detection equipment. Though people
cannot see, smell or taste H2 gas
under normal conditions, gas detection
equipment can sense a leak before
it ignites, increasing the possibility
of stopping a leak before it causes
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Chemical Engineering April 2020

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