Hypoxic air technology for fire prevention, also known as oxygen reduction system (ORS), is an

active fire protection 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. Categories of active fi ...

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.

Description

In a volume protected by hypoxic air, a normobaric hypoxic atmosphere is continuously retained: hypoxic means that the

partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas as if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal g ...

of the oxygen is lower than at the sea level, normobaric means that the

barometric pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1013.25 millibars, 7 ...

is equal to the barometric pressure at the sea level. Usually 1/4 to 1/2 of the

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements ...

contained in the

air The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...

(that is, 5 to 10% of the air) is replaced by the same amount of

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

: 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. 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.

Design and operation

Hypoxic air for fire prevention - concept

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 Infiltration is the unintentional or accidental introduction of outside air into a building, typically through cracks in the building envelope and through use of doors for passage. Infiltration is sometimes called air leakage. The leakage of room ...

, 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 sensor An oxygen sensor (or lambda sensor, where lambda refers to air–fuel ratio#Air–fuel equivalence ratio (λ), air–fuel equivalence ratio, usually denoted by λ) or probe or wikt:sond, sond, is an electronics, electronic device that measures th ...

s 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. 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. 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. 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.

Combined use of hypoxic air for fire prevention

Hypoxic air fire prevention systems can also be used for purposes other than fire prevention, for example: * High altitude training * Health * Preserving artifacts and objects from degradation or

oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or ...

* Preserving food from deterioration, commonly known as modified atmosphere packaging. Combining fire prevention, indoor climate and reduction of artefacts/food degradation is a completely new approach for a fire safety system.

Applications

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: *

Data centers A data center (American English) or data centre (British English)See spelling differences. is a building, a dedicated space within a building, or a group of buildings used to house computer systems and associated components, such as telecommun ...

/ ICT facilities * Storage of high value items *

Archives An archive is an accumulation of historical records or materials – in any medium – or the physical facility in which they are located. Archives contain primary source documents that have accumulated over the course of an individual o ...

* Freezer and cold storage * Large warehouses * Paper mills * Heritage applications * Telecom * Electrical substation * Utilities * Document Storage * High-bay Warehouses The reduction of artifact degradation and food deterioration is a plus for applications like food warehouses, storage and archives.

Effects on health

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. However, hypoxic air is considered by some to be safe to breathe for most people. 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''.” 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 Pressurized

aircraft cabin An aircraft cabin is the section of an aircraft in which passengers travel. Most modern commercial aircraft are pressurized, as cruising altitudes are high enough such that the surrounding atmosphere is too thin for passengers and crew to breat ...

s are typically maintained at 75 kPa, the pressure found at 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: * AI, Arbeitsinspektorat; * SUVA, Schweizerische Unfallversicherungsanstalt; * DGUV, Deutsche Gesetzliche Unfallversicherung; * UIAA, Medical commission of Union Internationale Des Associations D’Alpinisme.

Applicable standards and guidelines, system verification

* UL 67377 Oxygen Reduction Fire Prevention System Units * BSI PAS 95:2011 - Hypoxic air fire prevention systems. Specification * VdS 3527en:2007 - Inerting and Oxygen Reduction Systems, Planning and Installation *

Austrian Standards International Austrian Standards International (formerly german: Österreichisches Normungsinstitut), abbreviated ASI, is a standards organization and the ISO member body for Austria. History Its predecessor organization, the ''Österreichischer Normenaus ...

** ÖNORM F 3073: Planning, engineering, assembly, commissioning and servicing of oxygen reduction systems ** ÖNORM F 3007: Oxygen reduction system ** ÖNORM F 3008: Oxygen reduction system - CIE UNIT control unit *TRVB S 155: Engineering, installation and operation requirements for oxygen reduction systems using nitrogen in buildings from a fire prevention technology standpoint * EN 16750:2017 Fixed firefighting systems — Oxygen reduction systems — Design, installation, planning and maintenance * ISO 20338:2019 Oxygen reduction systems for fire prevention — Design, installation, planning and maintenance 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

References

{{Fire protection Active fire protection Safety equipment Fire suppression Industrial gases