CONFERINŢA SUDURA 2021
Reşiţa 22-23 aprilie 2021
TRAINING OF PERSONNEL WORKING IN ENVIRONMENTS WITH A
HIGH RISK OF FIRE AND EXPLOSION DUE TO OXYGEN
Bodea Marius1, Technical University of Cluj, Richard Molnar2, Linde Gas Romania
1mbodea@stm.utcluj.ro, 2richard.molnar@linde.com
Abstract. Many industrial fields are using different combustible and explosive
substances in the fabrication processes. Flammable gases, vapors, liquids, aerosols,
dusts and their mixtures with air can form potentially explosive atmospheres or fires
events. The working personnel in welding fabrication, petrochemical industry,
medical care and others industries should be aware of the dangers related to the
oxygen rich atmosphere. This paper provides an overview of the risks which could
trigger explosions or fires, in oxygen rich environments and underlines lack of
awareness of the staff over these risks and their poor knowledge on safety and
security measures. Recent events in Romania and in other countries in the world
have shown that fires in oxygen rich atmosphere are extremely dangerous, fast
developing, causing life loss and important material prejudices. Some of the causes
that have produced fires in hospitals remain unidentified until today, and represent
serious threats for these medical institutions that could repeat the same mistakes.
1. Introduction
Gaseous oxygen is colorless, odorless and tasteless; thus, it can not be detected by
normal human senses. In addition, the oxygen does not give any obvious
physiological effects that could alert the personnel about the presence of oxygen
enrichment atmosphere [4]. The normal oxygen concentration in atmospheric air is
approximately 21% by volume. In the United States regulations, the oxygen-enriched
atmosphere is defined for an environment containing more than 23.5% oxygen by
volume. In oxygen-enriched atmosphere, the reactivity of oxygen significantly
increases the fire risk, the combustion process being strongly accelerated [1-4].
Oxygen is widespread used in a variety of industries as an industrial gas. For
instance, in the petrochemical industry, the oxygen is used for partial oxidation of
gaseous and liquid organics. In the steel industry, the oxygen is used for steel
refining, while in the metal fabrication industry the oxygen is used to weld, cut, braze
and in silver-soldering. In the mining industry, the oxygen is used to refine copper,
gold and other metals. Oxygen is also widely used for secondary treatment of both
municipal and industrial wastewaters, while for tertiary water treatment is used
ozone. Ultra-high purity oxygen atmosphere is used in the microchips manufacturing
in the semiconductor industry, in order to avoid the surface chip contamination with
impurities [1]. The paper and pulp industry uses extensive amounts of oxygen or
ozone in the bleaching and delignification processes as an alternative to chlorine. In
the space programs, the oxygen plays a major role for life support during different
missions. The oxygen is widely used in large and small factories, automobile repair
shops, in home workshops but also in hospitals, in special intensive care units (ICU)
or at home for oxygen therapy. Just in US alone, more than 1.5 million adults use
supplemental oxygen for a variety of respiratory disorders to improve their quality of
life and prolong survival [6].
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As the population continues to age, the demand for oxygen home therapy will rise,
especially after the Covid 19 pandemic that have impacted more than 107.9 million
of people across the world (reference time 11 February 2021, Coronavirus Pandemic
Real Time Counter, World Map). As a result, many patients would require long-term
medical treatment for recovery, including home oxygen therapy. Many patients have
reported symptoms that last weeks or months after the infection has been gone. This
have been called the post-Covid19 syndrome or "long Covid", source NHS.
Before the pandemic Covid19, just in US alone, the home oxygen use was involved
in 182 home fires, 46 deaths, and 60 injuries annually [7]. Those numbers are
expected to grow significantly in the near future because of the increasing number of
patients that would need oxygen support at home or in hospitals. In an oxygen-rich
environment, even a simple spark from static electricity can lead to volatile fire
conditions that are dangerous to patients, their caregivers, and firefighters
responding to the fire [7]. Accordingly, to the National Institutes of Health (NIH),
nearly 12 million adults have been diagnosed with Chronic Obstructive Pulmonary
Disorder (COPD) and 120,000 people die each year only in US. The data published
by the Global Asthma Network (GAN); it shows that asthma affects nearly 334 million
people worldwide. The increasing patient population is expected to boost the
demand for oxygen therapy, especially in the Covid19 pandemic context. The rising
prevalence of COPD, which is the fifth leading cause of mortality is driving the
clinical urgency treatment to contribute to the expansion of the oxygen therapy [8].
In Romania, there were recently two major fire incidents in Covid19 hospitals and the
environment where the oxygen therapy was used was a major factor for the fire
ignition. On 14 November 2020, a fire broke out in the Covid-19 ward of the Piatra
Neamț Emergency Hospital killing ten people and injuring four others, including two
doctors. Three months later, another major fire started at Matei Balş Hospital, which
is another Romanian hospital for Covid19 patients. This time, more than 10 patients
lost their lives, four of them in the fire event and the others, in the next days after the
fire. Another fire in a Romanian hospital has killed four newborns at Giulești
Maternity Hospital in august 2010, also due to oxygen related security problems.
From the incidents above, it becomes very clear that oxygen enrichment atmosphere
represents a very dangerous environment that requires special protective measures.
Fig.1 Forecast of the oxygen therapy market size in US [8].
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The global oxygen therapy market size was estimated at USD 7.09 billion $ in 2015
and is anticipated to grow up to 18.2 billion $ until 2024, Fig. 1.
Deaths per 100 000 population (2008–2010)
2,5
2
1,76
1,5
1
0,5
0
Fig.2 Death rates from all fires across Europe for 100.000 population, Data from
WHO [2].
From Figure 2, it can be noticed that Romania presents the second death rate toll
due to fire incidents, after Finland. To put the Figure 2 in another perspective,
annually in UK are recorded about 30 000 house fires in a population of 55 million
people, which give an incidence of 0.06% fires per citizen [2]. Romania has almost
three times more deaths caused by fires, than are reported in UK. The population
awareness about the dangers related to oxygen use must be urgently addressed in
order to reduce the fire incidents in hospitals, homes and industrial units.
2. Fire causes in oxygen-rich environment
For a fire or explosion to occur, three elements are required: combustible material,
oxygen, and an ignition source. Most causes of oxygen fires are related to improper
operation and maintenance of oxygen systems, incorrect design of oxygen systems
and using of incompatible materials or equipment’s with oxygen service.
Fires burn hotter and faster in oxygen-enriched atmospheres so usually
nonflammable things can ignite at lower temperatures. In oxygen-enriched
atmospheres, a common combustible material that most directly affects the safety of
personnel are clothes. All clothing materials will burn fiercely in an oxygen-enriched
atmosphere. Oil and grease are particularly hazardous in the presence of oxygen as
they can ignite extremely easily and burn with explosive violence. The atmosphere
can be enriched with oxygen due to different causes: from leaking pipe connections
or flanges, or by using improper equipment in confined spaces, insufficient
ventilation in medical ICU, by desorption process when the oxygen is released from
absorbents materials like silica gel or others insulation materials that were warmed at
the room temperature etc.
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The most frequently ignition causes in home environment related to oxygen use are:
tobacco smoking, burning substances, naked flames (matches, lighters, etc.), even
the electronic cigarettes, oil heaters, flammable materials, cleaning fluids, paint
thinners, petroleum-based creams or aerosols, alcohols, sparks grinders, children's
toys, some electric shavers, high-frequency short-wave home appliances, hair dryers
etc. During oxygen therapy at home, the clothes and the hair becomes saturated in
oxygen and any ignition sources from above could trigger a violent fire.
The typically ignition sources in an industrial environment are open flames, cutting
and welding, hot surfaces, radiant heat, lightning, smoking, spontaneous ignition,
frictional heat, adiabatic compression of oxygen, sparks, static electricity, electrical
sparks, stray currents, ovens, furnaces, heating equipment and pyrotechnic
materials. The presentation of all the ignition sources is beyond the paper purpose
so further we’ll discuss only about the static electric discharges, frictional heat and
adiabatic compression of oxygen.
2.1. Electrostatic discharge (ESD)
Some of the causes that have produced fires in Romanian hospitals remained
unknown until today (e.g. the fire from Piatra-Neamţ emergency hospital). It seems
very probable that in some of the cases the fire was ignited by an ESD phenomena.
In media and in the press, it was speculated that the trigger factor of the fires in
hospitals it was the overcharged power grid due to the medical equipment. This
assumption could be a plausible cause, but in such cases, it must exist physical
proofs that support this scenario. It is very unlike that the overcharge of the power
grid hospital could come from the patient phones or tablets connected to the electric
grid as it was presented in media. In the ESD scenario, the fire ignition does not
imply the presence of an open heat source, or a short-circuit in the electric power
grid as it was considered until now. Every year 40 billion $ losses are reported in the
electronics industry only, due to ESD phenomena. Also, from all malfunction causes
in all electronic industry, a 25% is attributed to ESD phenomena.
a
b
Fig. 3 Examples of ESD phenomena by a) separation and b) induction.
All materials could be sources for ESD and the discharge can occur in a variety of
forms. One of the most common is through human contact with metallic parts of
objects/equipment, when the charges accumulated on the human skin are
discharged in a few picoseconds.
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During the ESD, the current dissipates through a spark, seeking a low impedance
path to ground in order to equalize the electric potentials. In an ESD event, the
human body can generate static charge levels as high as 15,000 volts, just by
walking across a carpeted floor and 5,000 volts by walking across a linoleum floor.
The potential difference between a charged human body and an object retaining an
insignificant charge can range from a few hundred volts to as high as 30,000 volts
[10-13].
Fig.4 Polyethylene foam ignition due to ESD phenomena, “The Sun” [13].
In the Fig.4 is presented the fire ignition moment due to an ESD phenomena. A tiny
spark was created between the workman shoe and the truck metal lorry box, which
has ignited the butane gas released by the polyethylene foam, also known as pearl
cotton. The butane gas was released slowly in an enclosed space, inside the truck
cargo, from the polyethylene foam and just a minor spark produced by ESD was
enough to ignite violently the entire cargo in a ball of flames [13].
The ESD represents the main cause of fire ignition in industrial environment
characterized by presence of gas mixtures, like combustibles vapors-air, dust
particles-air, aerosols-air or others combination [11]. Experimental tests have shown
that saturated hydrocarbon gases and vapors require only 0.25 mill joule of stored
energy spark ignition for an optimum mixture with air [11]. In a potentially explosive
atmosphere, it is important to know the incendivity of the ESD discharge,
respectively the amount of minimum ignition energy required to start a fire or an
explosion [10-14].
The spark energy of an ESD event has usually tens of mill joules, released in a few
picoseconds and can be calculated with the eq. (1), where C is capacitance of the
body and U is the electric potential:
𝐸=
1
∙ 𝐶 ∙ 𝑈2
2
The human body ESD phenomenon is dependent upon skin-surface resistance,
human body capacity, clothing characteristics and the atmosphere relative humidity.
Positive charges are accumulating predominantly on the human skin, while the
negative charges are more specific to the synthetic materials. The amount of
electrostatic charge that can accumulate on any object is dependent on its capacity
to store a charge (capacitance). For example, the human body can store a charge
equal to 250 Pico farads, which corresponds to a potential up to 25,000V [11, 12].
CONFERINŢA SUDURA 2021
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In the surrounding atmosphere the materials contain at surface a certain amount of
moisture in equilibrium with the air. If the relative humidity of the atmosphere is over
60 % the materials will contain enough moisture to make theirs surface conductivity
higher enough to prevent static accumulations [11]. At any constant moisture
content, the relative humidity of an atmosphere decreases as the temperature is
raised and vice versa. In cold season, the relative humidity of the outside air may be
high, but the absolute humidity of the atmosphere is low. When the cold air is
brought indoor and heated, the relative humidity indoor becomes very low and by
consequence, the ESD phenomena increased significantly. Thus, the ESD is usually
more dangerous during wintertime, because static charges on the objects have less
opportunity to dissipate due to low relative humidity indoor and also, people are
wearing clothes more susceptible to ESD phenomena.
It is generally believed that wearing cotton clothes can prevent the accumulation of
static charges. This is true only when the air relative humidity is above 50%, but
when the relative humidity is decreasing under 40% the static charges of the cotton
fabric is increasing significantly. If the relative humidity becomes even lower (20%),
the electrostatic accumulations of the cotton fabric become even higher by
comparison to some synthetic fiber fabrics [12].
In oxygen-enriched atmospheres, in order to effectively prevent the electrostatic
discharge of the human body, the working personnel should be equipped with
special antistatic clothing and shoes, wrist or heel straps that are connected to the
ground (personnel grounding systems). Modern wireless or cordless wrist straps
eliminate static buildup without the need of a grounding cord that directly connects
the workers to a ground circuit.
2.2. Wrong manipulation of the oxygen equipment
This section is referring only to the frictional heat, oxygen adiabatic compression and
equipment contamination with oil/organic compounds. There can be other faulty
operations, but also is beyond the paper limits to discuss all others scenarios.
Fires involving high-pressure oxygen regulators, cylinders and other metal
equipment are very rapid and violent events. In this cases, the common ignition
mechanisms involve particle and mechanical impact, mechanical friction, flow
friction, adiabatic compression, fresh metal exposure and organic contaminants.
The fire can start inside of an oxygen cylinder valve or regulator by a kindling chain
reaction. The heat generated e.g. by friction or by adiabatic compression of oxygen
is enough to ignite a more flammable material, that will ignite further a less
flammable material, until the ignition temperature of the regulator metal parts is
reached, as is illustrated in the Fig. 4.
Oxygen cylinder valves should be opened slowly to allow a gradually increase of
pressure inside regulator passages, reducing the oxygen adiabatic compression
effect. That would minimize the amount of heat developed by mechanical friction,
particle impact or adiabatic compression, allowing the heat dissipation within the
regulator before the ignition temperatures of metallic materials are reached.
CONFERINŢA SUDURA 2021
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Energy
Ignition of
valve body
basic
energy
inside the
valve
Ignition of
grease, oil
Ignition of
non-metallic
parts
Ignition of
thin metallic
(chips)
Time
Fig.4 Kindling chain reaction for fire ignition inside an oxygen cylinder valve.
As combustible materials in the kindling chain reaction could be mentioned:
grindings from the oxygen cylinder valve, particles from oxides or corrosion products,
others non-metallic contaminations, residual cleaning products, seals tapes,
lubricants and hydrocarbon contaminations. Even minor contaminants such as skin
and hair oils, hand lotions, hair care products, lubricants or some soap residues will
burn readily in 100% oxygen. Surfaces and parts that come into contact with oxygen
should be free of these contaminates at all times [5].
3. Physics phenomena in rapid fires and explosions. Case studies
Fire investigation reports have shown that in some conditions the fire can propagate
with unexpected speed and violence, which can lead to higher casualties. One of the
primary causes for such events could be the higher oxygen concentrations in the fire
place or others peculiar effects that can increase substantially the fire dynamics.
The trench effect is a combination of factors that can accelerate the fire propagation
on inclined surfaces. This is based on two combined phenomena: the Coandă effect
from fluid dynamics and the flashover concept from fire dynamics. The first report on
the trench effect was published in the scientific investigation of the King's Cross fire
in London (1987), when 31 people lost their lives [14]. The fire started on an
escalator containing combustible wood between the Piccadilly line platforms and the
ticket hall at King's Cross St. Pancras tube station. The sudden flashover was
attributed to the wood gas, mainly methane emitted from the pyrolysis of the wooden
escalator itself. When the concentration of the gas has reached a critical value, the
lower flammable limit, the gas suddenly catches fire in the presence of the flames,
resulting in an explosion.
The Coandă effect is the tendency of a fast stream of gases to bend towards, and to
adhere to the nearby surfaces. The flames heat the material further up, which lead
further to gas emissions, which auto ignite in a flashover event.
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Flashover is a sudden widespread fire, which occurs when most surfaces in a space
are heated until they emit flammable gases hot enough to auto-ignite. Before
flashover, flammable gases may be emitted but are too cool to ignite. The trench
effect occurs when a fire burns beside a steeply inclined surface.
A similar incident of flashover has been produced at Colectiv nightclub in Bucharest,
Romania, on 30 October 2015, killing 64 people [16]. The fire started due to a show
pyrotechnics consisting of sparkler firework candles, which has ignited the club's
flammable polyurethane acoustic foam, disposed on the vertical and ceiling walls. In
the incident has been reported an explosion [15], which in media was claimed as
being a proof for some conspiracy theories [17].
According to NASA agency, between 1962-1967 they had four fire incidents related
to electrical issues in hypobaric chambers, in pure oxygen atmosphere. Probably the
most known incident is the fire from Apollo Command Module 1, when three
astronauts lost their life. Just a few days later, two US Air Force Airman were killed in
another fire in pure oxygen hypobaric chamber [14].
In March 1961 the Russian cosmonaut Valentin Bondarenko was killed during a
routine training exercise in a pressure oxygen chamber, when he accidentally
dropped a cotton ball on a hot plate used for cooking. The incident was kept secret
to the public for 25 years [19].
Other fire events have been reported in diving bells, decompression chambers,
hypobaric chambers, clinical inside/outside of hyperbaric chambers, during medical
anesthesia operations, in ICU in hospitals.
4. Conclusions
o The oxygen-enriched atmosphere represents a very dangerous environment,
that could lead to fires and explosions if the protective measures are not
respected. The working space shall be thoroughly ventilated to maintain an
atmosphere of no greater than 23.5% oxygen;
o Absorbent materials, such as clothes or beddings, when saturated with oxygen,
will readily ignite. Persons who have been exposed to an oxygen-enriched
atmosphere shall not smoke or go near open flames, hot spots or sparks until
they have properly ventilated their clothes in a normal atmosphere for at least
15-20 minutes;
o An ignition factor could be the “electronic cigarettes”, which the European
Industrial Gases Association has declared to be unsafe to use with home
oxygen therapy;
o Oils and grease burn in an oxygen-enriched environment with explosive
violence. Ignitions can occur with oxygen equipment if it has been contaminated
with oil or grease;
o Preventing human body ESD phenomena can be accomplished by assurance of
the floor surfaces conductivity, by wearing of antistatic shoes and wearing of
antistatic work clothes. The workspace should have a relative humidity between
45% to 60%.
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o Maintenance of cylinders, valves, and regulators should be done only by trained
technicians using tools and facilities specially cleaned for oxygen service.
References
1. Bryan J. Coleman, Chairman NASA/Kennedy Space Center, FL, a.o. Technical
Committee on Oxygen-Enriched Atmospheres, Manual on Fire Hazards in
Oxygen-Enriched Atmospheres. NFPA 53M-1990, Volume 9, 1992, NF Codes.
2. Brendan G. Cooper, Home oxygen and domestic fires, Breathe, Volume 11, No
1, DOI: 10.1183/20734735.000815, 2015.
3. Air Products and Chemicals, Inc., Safetygram 33, The hazards of oxygen and
oxygen-enriched mixtures, 2014.
4. European Industrial Gases Association Aisbl, Fire Hazards of Oxygen and
Oxygen-Enriched Atmospheres, Doc 04/18, EIGA 2018.
5. United States Fire Administration, Special report: Fires Involving Medical Oxygen
Equipment - Report 107 of the Major Fires Investigation Project conducted by
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Testing & Failure Analysis, Los Angeles, California, USA/15-19 November 1993.
13. The Sun, 28 Jan 2019, Workman engulfed in flames after static from his SHOE
ignites lorry load of foam, video: https://www.youtube.com/watch?v=GjiU4VvUSPo
14. P.J. Sheffield, D.A. Desautels, Hyperbaric and hipobaric chamber fires: a 73year analysis, Undersea and Hyperbaric Medical Society Inc., 1997.
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https://www.nineoclock.ro/2016/01/04/colectiv-and-the-theory-of-conspiracy/
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