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ReviewPreventing explosions of hydrogen gas inhalers
Ryosuke Kurokawa1, #, Shin-ichi Hirano1, #, Yusuke Ichikawa1, Goh Matsuo1, Yoshiyasu Takefuji2, *1 MiZ Company Limited, Kamakura, Kanagawa, Japan
2 Faculty of Environment and Information Studies, Keio University, Fujisawa, Japan#These authors contributed equally to this work.
*Correspondence to: Yoshiyasu Takefuji, PhD, takefuji@sfc.keio.ac.jp.
orcid: 0000-0002-1826-742X (Yoshiyasu Takefuji)

Abstract
Production and excretion of hydrogen (H2) gas in human was reported in 1969, since then it has been regarded as non-toxic molecule. For
preventive and therapeutic medical uses, a possible treatment for cancer was reported and another article was published on how H2 acts as atherapeutic antioxidant by selectively reducing cytotoxic oxygen radicals. A variety of H2 gas inhalers have been available in the market for
hospital and home uses. However, H2 is odorless and flammable or explosive ignited by static electricity. We have examined the safety of avariety of H2 gas concentrations from the viewpoint of flammability and explosion. We have also measured concentrations of H2 gas inhalers
in the market respectively. This paper also details how to control H2 gas concentration for preventing explosions.
Key words: hydrogen gas; hydrogen concentration; explosion; detonation; flammability; static electricity; hydrogen gas inhaler; medicaluse; home use; market; safety
doi: 10.4103/2045-9912.266996
How to cite this article: Kurokawa R, Hirano S, Ichikawa Y, Matsuo G, Takefuji Y. Preventing explosions of hydrogen gas inhalers. MedGas Res. 2019;9(3):160-162.

INTRODUCTION

Production and excretion of hydrogen (H2) gas in human wasreported in 1969, since then it has been regarded as non-toxic
molecule.1 H2 was recently reported by Ohsawa et al.2 as apreventive and therapeutic antioxidant. However, in 2005,
2 years ago of the Ohsawa’s report, Yanagihara et al.3 at ourgroup reported that drinking of neutral H2-rich water produced
by electrolysis could effectively reduce the oxidative stressinduced by chemical oxidant in rats, indicating that this is apioneering research in H2 medicine. H2 has also been proposed
for treatment in various oxidative stress-related diseases anddamages.4-9 A variety of H2 gas inhalers have been available
in the market for clinical and home uses. However, H2 is odorless and flammable or explosive ignited by static electricity.
In the present study, we examined the safety of a variety ofH2 gas concentrations from the viewpoint of flammability andexplosion. In addition, we also measured concentrations of H2gas inhalers in the market respectively.

HOW DOES H2 GAS CONCENTRATION INFLUENCEEXPLOSION?

Taiyo Nippon Sanso Pure H2 gas G2 (Tokyo, Japan) was usedin the first experiment for testing explosions based on a varietyof H2 concentrations. The H2 concentration was measured by
New Cosmos Electric: XP-3140 (Osaka, Japan). In order toexamine the H2 gas concentrations with mixture of air, we havetested flammability and explosion under five H2 concentrations
respectively: 4%, 10%, 15%, 20%, and 100%. Under the H2concentration of 4% and 10%, no explosion/flammability wasdetected. Under the 15% and 100% H2 concentration, a small
explosion with small sound was detected which may not cause
a severe damage to user. Under the 20% H2 concentration, alarge explosion (detonation) was detected which may cause a160

severe damage to user. From this H2 concentration experiment,
we understood that the H2 concentration must be less than 10%.
In addition, we did a systematic search of Google Scholar andPubMed using the search terms (“hydrogen gas” and “explosion” or “detonation” and “concentration”) before initiating
this study on December 5, 2015, and we repeated this searchon August 5, 2019. In these searches, many papers describedthe explosive concentration of H2 gas in the mixture of H2 gas
and air as 4 to 75%.10,11 However, a few reports reported that
H2 does not explode if it is less than 10% when mixed with
air or oxygen.12-14 Therefore, our present experimental data aresupported by the latter reports.

MEASURING H2 CONCENTRATION OF H2 GAS INHALERS

New Cosmos Electric XP-3140 was used for measuring H2concentrations of H2 gas inhalers (15 products) in the market
respectively. In the measurement of H2 concentration, weused 5 apparatus and 1 apparatus for MHG-2000α and other14 apparatus respectively. Additionally, we confirmed that theresult of H2 concentration is correct in each product catalog.
Table 1 shows the result of measured H2 concentrations. Remember that H2 gas concentration over 10% is explosive anddangerous. Consumer safety regulations for H2 gas inhalers
are immediately required for protecting users in order to avoid
dangerous explosions.

H2 GAS IGNITED BY STATIC ELECTRICITY

We must examine a risk of static electricity ignition. According to Danger of H2 Gas Explosion, and Prevention Measures(Division of Gas Safety, Institute of Chemical Technology,National Institute of Advanced Industrial Sciences and Technology, Japan), the minimum ignition energy of H2 gas is 0.02
mJ.15 According to electrostatic sensitivity of H2 by Mizuki© 2019 Medical Gas Research | Published by Wolters Kluwer - Medknow

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Kurokawa et al. / Med Gas Res

Table 1: Hydrogen (H2) gas inhalers (products) in themarket
Product nameSupplier

MHG-2000α

MiZ Co., Ltd.,
Kanagawa, Japan
Helix Japan Co.,Ltd., Tokyo,JapanJWS International
Corp., Tokyo,Japan
Brain Hokkaido
Co., Ltd.,
Hokkaido, Japan
Univers Co., Ltd.,Tokyo, JapanOPS Inc., Tokyo,Japan
Asklepios
Medical Co., Ltd.,Tokyo, Japan
ISMZ Co., Ltd.,
Osaka, Japan
Kenko Shien
Center Co., Ltd.,
Aichi, Japan
Kenko Co., Ltd.,
Gifu, Japan
Eco
Higashinippon
Co., Ltd.,
Fukushima, Japan
Earth Engineering
Co., Ltd.,
Fukuoka, Japan
Pal Corporation,Tokyo, Japan
Kanon Co., Ltd.,
Osaka, Japan
MYC Co., Ltd.,
Kumamoto, Japan

Hycellvator
H2 Life
HydroPower
HydroUni
HydrogenGenerator
AMS-H
La Briller
Luxe
Hydrogen
Inhaler (Tabletop type)
Suiso Care
PHG-150TA

Suisonia
HydroRich
Hydrogen
Generator
MYC HydroOne

H2 concentration(%)
Method
6.6±0.2*

Electrolysis

66#
66#
66#
66#
66#
66#

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we recently demonstrated that the detonation limit is less than
10% by our experiment and literature search.17 Therefore, wedeveloped the safe H2 gas supply system (MHG-2000α). As
shown in Figure 1, inhalation gas was prepared by mixing H2gas with air, where the H2 gas was produced 140 mL/min by
the electrolysis of water, and the concentration was controlled
about 6.0–7.0% under the detonation limit of the mixture of
H2 gas and air (below 10%). Moreover, this H2 gas supply
system consists of raw water in an electrolyzed chamber, thediaphragm and the electrode plate. H2 gas is directly generated
from the electrode plate and cathode, based on the interaction
between the fan on the water surface, the cathode gas and thediluted air. Thus, the concentration of H2 gas near the cathodeduring electrolysis is always maintained below 10%, the lowerlimit of explosion. MHG-2000α has the new remarkable function system, which is indicated H2 gas concentration, calculated
from the current value and diluent gas. When it will be morethan 10% of H2 gas concentration, the electrolysis of water
will be stopped immediately for safe.

98
99
99
99

ND

Pyrolysis

99

Chemicalreaction99
99

Note: *Data are expressed as the mean ± SD of 5 apparatus. #H2 and O2 gas
mixed type. ND: Not detected.

Yamakuma (National Institute of Occupational Safety andHealth, Japan), electrostatic charge of the human body is 0.05
mJ with 1.0 kV human charging potential.16 When assuming
human is a capacitor of 90 pF, 1.0 kV (0.05 mJ) to 2.5 kV(0.28 mJ) human charging potential cannot be sensed by us atall. In other words, it is highly possible to easily ignite H2 gas
by static electricity without our recognition. 0.02 mJ ignitionenergy can be easily satisfied in hospital and at home. In fact,
we examined to observe if an explosion would occur by alighter flame or static electricity close to the outlet of H2 gas
inhaler using H2 life, La Briller Luxe, or HydRich respectively.
As a result, large explosions (detonation) were detected withthese three products (data not shown).

CONTROLLING H2 GAS CONCENTRATION

Although it is well known that the H2 gas concentration indetonation of the mixture of H2 gas and air is less than 4%,
Medical Gas Research ¦ September ¦ Volume 9 ¦ Issue 3Figure 1: Apparatus for hydrogen (H2) gas inhalation (MHG-2000α).
Note: The inhalation gas is prepared by mixing H2 gas with air, where H2 gas wasproduced by the electrolysis of water, and the concentration is controlled under
the detonation limit of the mixture of H2 gas and air.

In usual conditions, H2 gas does not explode at a concentration of 10% or less. Since H2 is a colorless gas with no taste orodor, we do not know the actual concentration of H2 gas produced by the H2 gas inhaler. Therefore, using a H2 gas inhaler
carries a risk of explosion. In one inhaler such as Suisonia,
we could not confirm H2 gas generation at all. Most of H2gasinhalers have some risks of explosion except MHG-2000αand Suisonia. As of today, there is no legislation to regulate
proper production and/or use of H2 gas inhalers. We should befully aware of the risks of H2 gas inhalers to prevent serious
accident involving human life. To our knowledge, this is thefirst paper demonstrating the explosion risk of H2 gas inhalers in the market. The proposed results will be useful for theinformation of safe H2 gas inhalers.
Acknowledgements
The authors are grateful to Mr. Fumitake Satoh, Ms. Yoko Satoh, Dr.
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Kurokawa et al. / Med Gas Res

Yi-Da Hsieh and Mr. Masatsugu Saitou (MiZ Co. Ltd., Japan) for
their excellent advices in the writing of this manuscript.
Author contributions
Study design and data analysis: RK, SH; manuscript writing andfigures preparation: SH, GM, YT; H2 gas inhaler preparation andmeasurement: RK; data collection and study guidance: YT, YI, GM.
All authors read and approved the final manuscript.
Conflicts of interest
The authors have no conflicts of interests to declare.
Financial support
None.
Copyright license agreement
The Copyright License Agreement has been signed by all authors
before publication.
Plagiarism check
Checked twice by iThenticate.
Peer review
Externally peer reviewed.
Open access statement
This is an open access journal, and articles are distributed under
the terms of the Creative Commons Attribution-NonCommercialShareAlike 4.0 License, which allows others to remix, tweak, andbuild upon the work non-commercially, as long as appropriate credit
is given and the new creations are licensed under the identical terms.

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Received: May 29, 2019
Reviewed: May 30, 2019
Accepted: July 29, 2019

Medical Gas Research ¦ September ¦ Volume 9 ¦ Issue 3