Hypoxic air technology for fire prevention, also known as oxygen reduction system (ORS), is an active fire protection technique based on a permanent reduction of the oxygen concentration in the protected rooms. Unlike traditional fire suppression systems that usually extinguish fire after it is detected, hypoxic air is able to prevent fire.
In a volume protected by hypoxic air, a normobaric hypoxic atmosphere is continuously retained: hypoxic means that the partial pressure of the oxygen is lower than at the sea level, normobaric means that the barometric pressure is equal to the barometric pressure at the sea level. Usually 1/4 to 1/2 of the oxygen contained in the air (that is, 5 to 10% of the air) is replaced by the same amount of nitrogen: as a consequence a hypoxic atmosphere containing around 15 Vol% of oxygen and 85 Vol% of nitrogen is created. In a normobaric hypoxic environment, common materials cannot ignite or burn when exposed to a localized small scale ignition source. [1] A reduction of the oxygen level to 15% does not achieve conditions where a fire cannot occur or is extinguished. However, it reduces the probability of a fire occurring by increasing the ignition energy needed, and there are also indications of increased ignition times. [2]
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Air with a reduced oxygen content is injected to the protected volumes to lower the oxygen concentration until the desired oxygen concentration is reached. Then, because of air infiltration, the oxygen concentration inside the protected volumes rises: when it exceeds a certain threshold, low-oxygen air is again injected to the protected volumes until the desired oxygen concentration is reached. Oxygen sensors are installed in the protected volumes to continuously monitor the oxygen concentration.
The exact oxygen level to retain in the protected volumes is determined after a careful assessment of materials, configurations, and hazards. [3] Tables list ignition-limiting oxygen thresholds for some materials. Alternatively, the ignition-limiting threshold is determined by performing a proper ignition test described in BSI PAS 95:2011 Hypoxic air fire prevention systems specification. [4]
Smoke detectors are installed in protected volumes because, similar to gas suppression systems, hypoxic air does not prevent smoldering and pyrolyzing processes.
Air with low oxygen concentration is produced by hypoxic air generators, also known as air splitting units. There are three different types of hypoxic air generators: membrane-based, PSA-based, and VSA-based. VSA-based hypoxic air generators usually have a lower energy consumption compared to PSA-based and membrane-based generators. Hypoxic air generators can be located inside or outside the protected rooms. Hypoxic air systems can be integrated with the building management system and can include systems to recover the heat generated by the hypoxic air generator that, would otherwise be wasted. [5]
Air with low oxygen concentration is transported to the protected volumes through dedicated pipes or, more simply, via an existing ventilation system. In the latter case, dedicated pipes or ducts are not required.
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The benefits of preventing a fire instead of suppressing it makes hypoxic air suitable for applications where a fire would cause unacceptable damage. Unlike traditional fire-suppression systems, dedicated pipes or nozzles are not required.
Hypoxic air for fire prevention are used in[ citation needed ]:
The reduction of artifact degradation and food deterioration is a plus for applications like food warehouses, storage and archives.
Hypoxic air fire prevention systems can also be used for purposes other than fire prevention, for example:
Combining fire prevention, indoor climate and reduction of artefacts/food degradation is a completely new approach for a fire safety system.
Fire-prevention systems which result in the oxygen content being less than 19.5% are not permitted for occupied spaces without providing employees supplemental respirators by federal regulation (OSHA) in the United States. [6]
However, hypoxic air is considered by some to be safe to breathe for most people. [7] Medical studies have been undertaken on this topic. Angerer and Novak's conclusion is that "working environments with low oxygen concentrations to a minimum of 13% and normal barometric pressure do not impose a health hazard, provided that precautions are observed, comprising medical examinations and limitation of exposure time." [8] Küpper et al. say that oxygen concentration between 17.0 and 14.8% does not cause any risk for healthy people by hypoxia. It also does not cause risks for people with chronic diseases of moderate severity. The ability for strenuous work is reduced as the concentration decreases with the time that exertion can be sustained becoming very low below these levels, below around 17% it may be necessary to take breaks outside the environment if more than 6 hours is to be spent inside, especially if any physical exertion is performed [9]
Pressurized aircraft cabins are typically maintained at 75 kPa, the pressure found at 2,500 m (8,200 ft) altitude, resulting in an oxygen partial pressure of about 16 kPa, which is the same as a 15% oxygen concentration in a hypoxic-air application at sea-level pressure. However, passengers are sedentary and crew members have immediate access to supplemental oxygen.
Hypoxic air is to be considered clean air and not contaminated air when assessing oxygen depletion hazards.
Information relating access to the protected areas i.e. oxygen-reduced atmosphere are illustrated:
Inspection body accreditation criteria are established according to ISO/IEC 17010 for third party verification of hypoxic air fire prevention system conformance to BSI PAS 95:2011 and VdS 3527en:2007 [12]
Hypoxia is a condition in which the body or a region of the body is deprived of adequate oxygen supply at the tissue level. Hypoxia may be classified as either generalized, affecting the whole body, or local, affecting a region of the body. Although hypoxia is often a pathological condition, variations in arterial oxygen concentrations can be part of the normal physiology, for example, during strenuous physical exercise.
Dead zones are hypoxic (low-oxygen) areas in the world's oceans and large lakes. Hypoxia occurs when dissolved oxygen (DO) concentration falls to or below 2 mg of O2/liter. When a body of water experiences hypoxic conditions, aquatic flora and fauna begin to change behavior in order to reach sections of water with higher oxygen levels. Once DO declines below 0.5 ml O2/liter in a body of water, mass mortality occurs. With such a low concentration of DO, these bodies of water fail to support the aquatic life living there. Historically, many of these sites were naturally occurring. However, in the 1970s, oceanographers began noting increased instances and expanses of dead zones. These occur near inhabited coastlines, where aquatic life is most concentrated.
Generalized hypoxia is a medical condition in which the tissues of the body are deprived of the necessary levels of oxygen due to an insufficient supply of oxygen, which may be due to the composition or pressure of the breathing gas, decreased lung ventilation, or respiratory disease, any of which may cause a lower than normal oxygen content in the arterial blood, and consequently a reduced supply of oxygen to all tissues perfused by the arterial blood. This usage is in contradistinction to localized hypoxia, in which only an associated group of tissues, usually with a common blood supply, are affected, usually due to an insufficient or reduced blood supply to those tissues. Generalized hypoxia is also used as a synonym for hypoxic hypoxia This is not to be confused with hypoxemia, which refers to low levels of oxygen in the blood, although the two conditions often occur simultaneously, since a decrease in blood oxygen typically corresponds to a decrease in oxygen in the surrounding tissue. However, hypoxia may be present without hypoxemia, and vice versa, as in the case of infarction. Several other classes of medical hypoxia exist.
Altitude training is the practice by some endurance athletes of training for several weeks at high altitude, preferably over 2,400 metres (8,000 ft) above sea level, though more commonly at intermediate altitudes due to the shortage of suitable high-altitude locations. At intermediate altitudes, the air still contains approximately 20.9% oxygen, but the barometric pressure and thus the partial pressure of oxygen is reduced.
An altitude tent is a sealed tent used to simulate a higher altitude with reduced oxygen. Living or training at altitude causes the body to adapt to the lower oxygen content by producing more oxygen-carrying red blood cells and hemoglobin, thus causing the body to adapt to the higher altitude and enhancing performance when returning to a lower altitude. Mountain climbers can use them to avoid altitude sickness, and athletes can use them to enhance performance at lower altitudes.
Cerebral hypoxia is a form of hypoxia, specifically involving the brain; when the brain is completely deprived of oxygen, it is called cerebral anoxia. There are four categories of cerebral hypoxia; they are, in order of increasing severity: diffuse cerebral hypoxia (DCH), focal cerebral ischemia, cerebral infarction, and global cerebral ischemia. Prolonged hypoxia induces neuronal cell death via apoptosis, resulting in a hypoxic brain injury.
Hyperoxia occurs when cells, tissues and organs are exposed to an excess supply of oxygen (O2) or higher than normal partial pressure of oxygen.
Intrauterine hypoxia occurs when the fetus is deprived of an adequate supply of oxygen. It may be due to a variety of reasons such as prolapse or occlusion of the umbilical cord, placental infarction, maternal diabetes and maternal smoking. Intrauterine growth restriction may cause or be the result of hypoxia. Intrauterine hypoxia can cause cellular damage that occurs within the central nervous system. This results in an increased mortality rate, including an increased risk of sudden infant death syndrome (SIDS). Oxygen deprivation in the fetus and neonate have been implicated as either a primary or as a contributing risk factor in numerous neurological and neuropsychiatric disorders such as epilepsy, attention deficit hyperactivity disorder, eating disorders and cerebral palsy.
Freediving blackout, breath-hold blackout, or apnea blackout is a class of hypoxic blackout, a loss of consciousness caused by cerebral hypoxia towards the end of a breath-hold dive, when the swimmer does not necessarily experience an urgent need to breathe and has no other obvious medical condition that might have caused it. It can be provoked by hyperventilating just before a dive, or as a consequence of the pressure reduction on ascent, or a combination of these. Victims are often established practitioners of breath-hold diving, are fit, strong swimmers and have not experienced problems before. Blackout may also be referred to as a syncope or fainting.
Active fire protection (AFP) is an integral part of fire protection. AFP is characterized by items and/or systems, which require a certain amount of motion and response in order to work, contrary to passive fire protection.
Hypoxia means a lower than normal level of oxygen, and may refer to:
The effects of high altitude on humans are mostly the consequences of reduced partial pressure of oxygen in the atmosphere. The medical problems that are direct consequence of high altitude are caused by the low inspired partial pressure of oxygen, which is caused by the reduced atmospheric pressure, and the constant gas fraction of oxygen in atmospheric air over the range in which humans can survive. The other major effect of altitude is due to lower ambient temperature.
Latent hypoxia is a condition where the oxygen content of the lungs and arterial blood is sufficient to maintain consciousness at a raised ambient pressure, but not when the pressure is reduced to normal atmospheric pressure. It usually occurs when a diver at depth has a lung gas and blood oxygen concentration that is sufficient to support consciousness at the pressure at that depth, but would be insufficient at surface pressure. This problem is associated with freediving blackout and the presence of hypoxic breathing gas mixtures in underwater breathing apparatus, particularly in diving rebreathers.
A hypoxicator is a medical device intended to provide a stimulus for the adaptation of an individual's cardiovascular system by means of breathing reduced oxygen hypoxic air and triggering mechanisms of compensation. The aim of intermittent hypoxic training or hypoxic therapy conducted with such a device is to obtain benefits in physical performance and wellbeing through improved oxygen metabolism.
Nitrogen generators and stations are stationary or mobile air-to-nitrogen production complexes.
The limiting oxygen concentration (LOC), also known as the minimum oxygen concentration (MOC), is defined as the limiting concentration of oxygen below which combustion is not possible, independent of the concentration of fuel. It is expressed in units of volume percent of oxygen. The LOC varies with pressure and temperature. It is also dependent on the type of inert (non-flammable) gas.
Hypoxia refers to low oxygen conditions. For air-breathing organisms, hypoxia is problematic. But for many anaerobic organisms, hypoxia is essential. Hypoxia applies to many situations, but usually refers to the atmosphere and natural waters.
Fish are exposed to large oxygen fluctuations in their aquatic environment since the inherent properties of water can result in marked spatial and temporal differences in the concentration of oxygen. Fish respond to hypoxia with varied behavioral, physiological, and cellular responses to maintain homeostasis and organism function in an oxygen-depleted environment. The biggest challenge fish face when exposed to low oxygen conditions is maintaining metabolic energy balance, as 95% of the oxygen consumed by fish is used for ATP production releasing the chemical energy of nutrients through the mitochondrial electron transport chain. Therefore, hypoxia survival requires a coordinated response to secure more oxygen from the depleted environment and counteract the metabolic consequences of decreased ATP production at the mitochondria.
Oxygen compatibility is the issue of compatibility of materials for service in high concentrations of oxygen. It is a critical issue in space, aircraft, medical, underwater diving and industrial applications. Aspects include effects of increased oxygen concentration on the ignition and burning of materials and components exposed to these concentrations in service.
In fire and explosion prevention engineering, inerting refers to the introduction of an inert (non-combustible) gas into a closed system to make a flammable atmosphere oxygen deficient and non-ignitable.
