H2Tech - Q1 2021 - 39

MEASUREMENT AND INSTRUMENTATION
Additionally, while they need calibration less frequently than
the pellistor/catalytic bead sensors, NDIR sensors still require
calibration at least yearly. These sensors do perform better than
pellistor/catalytic bead sensors in certain situations, but since
NDIR is a proprietary technology, it can be expensive.
Detecting hydrogen and other hazardous gases. Detecting
hazardous gases is crucial in many industries, such as mining and
petroleum extraction/production. Global demand for H2 continues to increase year after year to meet the needs of these and other industries. The use of H2 has tripled since the 1970s, and the
total global market value is expected to exceed $160 B by 2026.
The increased use of H2 also raises the potential for significant events that risk the health and safety of employees and
expose businesses to financial liability, especially if leaks go undetected:
* Exposure to even low H2 concentrations can result in
nausea, headaches, delirium, tremors, convulsions
and irritation of the skin and eyes. At high
concentrations, an individual can rapidly lose
consciousness. The effects of H2 on the central nervous
system can cause death in a short amount of time.
* H2 is flammable and combustible, and it is frequently
used in the same vicinity as other flammable materials
and gases. It has lower ignition energy than gasoline
or natural gas and, once ignited, can spread rapidly
or lead to dangerous fires or explosions.
* Stringent safety and environmental standards have
been enacted in most areas, including regulations
that require gas detection procedures when exposure
is possible. Failure to comply with these regulations could
result in penalties and fines.
To protect the workplace, workers and the profitability of the
business, employers in industries that utilize H2 gas must have
reliable and accurate gas detection sensors. Recent innovations
have allowed the development of technology that is superior to
pellistor/catalytic bead and NDIR sensors.

MEMS-based hydrogen gas sensors. A new sensor that

uses a micro-electromechanical system (MEMS) transducer
represents an innovative change in gas detection technology.
The development of these sensors was driven by the need to
detect hazardous gases, particularly H2 , more accurately and
to mitigate the risks to employees and businesses.
The initial research was conducted through a partnership
with the University of Nevada in Reno, the U.S. Department
of Defense and the U.S. Defense Advanced Research Projects
Agency (DARPA). The research team wanted to take sensors
from an atomic-force microscope and use them for sensing
molecules. Due to their small size, the sensors were exceptionally sensitive. The first commercial effort to implement
this technology was the Small Business Innovation Research
(SBIR) project, " Chemical and explosive vapor detection in
shipping containers with remotely accessed microcantilever
array sensors. " This project's vision was to create a sensor
installed within shipping containers, capable of sniffing out
threats such as chemical weapons, explosives or dirty bombs.
Ultimately, the research team realized that these MEMS
sensors could deliver better results than both pellistor/catalytic bead and NDIR sensors, without the drawbacks, for
sensing multiple gases simultaneously. The MEMS transducer
measures changes in the thermal properties of the surrounding air and gases in its proximity, using an embedded heater
and thermometer. The MEMS-based H2 sensors display excellent performance in detecting H2 down to concentrations
of 0.2 vol%.
These sensors can measure the concentration of flammable or combustible gases, as well as gas mixtures, and classify
the detected gas sample into H2, an H2-containing mixture,
methane, light gas, medium gas or heavy gas. The sensors can
detect the full range of flammable gases within seconds, from
H2 to heavy hydrocarbons. In addition, these sensors have a
longer life expectancy (up to 5 yr) and do not need to be recalibrated in the field; a single calibration can deliver an accurate measurement of 15 different gases. With NDIR or pellis-

TABLE 1. Relative performance in key categories of the three main sensor types
Pellistor/catalytic bead

NDIR

MEMS

Responds to a full range of flammable gases, including H2

Yes

Operates without damage up to 100% vol/vol
gas concentrations

Yes

Real-time auto-calibration to full range of gases

Yes

Gas classification

Yes

Excellent

Good

Excellent

Poor

Excellent

Poor (0.25 yr)

Good (0.5 yr)

Excellent (never)

Lifetime

Poor (2 yr)

Excellent (5 yr)

Excellent (5+ yr)

Power consumption

Poor
(> 150 MW)

Ranging from poor (> 105 MW)
to excellent (< 5 MW)

Good
(< 20 MW)

Good/excellent

Failsafe, self-diagnostic capability

Yes

Cost

Low

High

Competitive

Environmental range
Poison resistance
Calibration interval

Response time

H2Tech | Q1 2021 39

H2Tech - Q1 2021

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