Chris Beh, Think Consulting

Oxygen Reduction Systems (ORS) utilise a process to lower the atmospheric oxygen levels of 21% below the ignition threshold for the items stored in an area (e.g. below 14%) – a proactive, preventative fire protection system unlike fire suppression, such as sprinklers, which are reactive (i.e. initiate only when a fire event occurs).

Typically, nitrogen is generated from ambient air using on-site pressure swing adsorption (PSA) units and introduced into the area to be protected. Uses for the technology has been in high-value occupancies where the use of traditional fire suppression technologies such as fire sprinklers is challenging due to space constraints and hydraulic design (e.g. for adequate pipe work), tight or congested storage, lack of established protection design methodologies, or need to avoid water or chemical residue damage.

Globally, there are more than 500 installations of these systems with applications in high-bay and freezer/cold store warehouses, datacentres and museums and libraries where valuable artifacts need protection from fire without exposure to extinguishing agents.

In New Zealand, the use of this technology has mainly been in high-bay, cold store warehouses with the popularity of the system slowly becoming recognised.

Firms considering installing ORS should consider the following which may influence both the acceptance (such as insurer) and the requirements imposed on facilities utilising this technology, noting this list is not exhaustive.

Design

• Undertake a risk-based design review of the system and process including operation, maintenance and health and safety.
• Ensure the operating oxygen level is correctly designed for the hazard class being stored.
• The protected area sealed and structurally suitable for maintaining reduced oxygen levels.
• The enclosure that contains the reduced oxygen environment is to be constructed of non-combustible material.
• This area is to maintain the oxygen design concentration for twelve hours with all operations shutdown and no nitrogen generation.
• The exterior enclosure that contains the reduced oxygen environment is to be protected from potential impact.
• The nitrogen generation system and control system is to be located in a non-combustible enclosure outside the area containing the reduced oxygen environment and appropriately sealed to prevent ingress or exposure to the reduced oxygen environment.
• ORS plant replicated (N+1) with sufficient redundant capacity to maintain target oxygen levels, including backup electrical generator and PLC 24-hour battery backup, availability of replica PLC, spare PLC programme and ease of access to.
• Automatic fire detection air sampling installed, 24/7 monitored and Fire Service connected.
• Oxygen sensors should be located in all key locations of the building with identification of potential dead spots or limited mixing.
• ORS building to be fire separated, either physically through distance (i.e. 10m to 12m), firewalls or sprinkler protection, from surrounding exposures such as other buildings or unprotected external fire sources or combustible or flammable storage.
• There is no NZ standard for ORS installation and so international standards such as ISO 20338 or EN 16750:2020 should be used.

Operation and Maintenance

• Continuous monitoring and control of oxygen levels and nitrogen plant operation with each external indication installed to display the lowest oxygen sensor value.
• Oxygen leakage rates over time recorded to determine if this is increasing or stable to determine if building condition remediation is required.
• Conduct building tightness test in accordance with NFPA 2001, ISO 14520, EN 15004, or other applicable code or standard.
• Documented plant preventative maintenance program formalised and contractor approved by the OEM.
• At least annual calibration of oxygen sensors.

Health and Safety

‘Safe’ exposure levels for personnel entering the ORS environment in the event of unplanned maintenance or in the response to a major event such as equipment failure, natural hazard or fire event is debated.

From a confined space perspective, most countries have a minimum oxygen concentration of 19.5% which includes Australia and New Zealand (e.g. AS/NZS 2865:2001). However, this is over the ignition threshold of the items stored (including packaging) which is typically below 14%,

A paper by Burtscher, M., et al. (2011), states that “Although millions of people are regularly or occasionally performing mountain sport activities, are transported by airplanes, and are more and more frequently exposed to short-term hypoxia in athletic training facilities or at their workplace, … there is no clear consensus on the level of hypoxia which is generally well tolerated by human beings when acutely exposed for short durations (hours to several days).”

A lack of data exists on a wide variety of people with varying physiologies, fitness levels, ages and conditions such as hyperthyroidism, diabetes, or neurological diseases such as epilepsy, operating at reduced oxygen atmospheres.

Medical screening, regular checks and monitoring of personnel entering atmospheres below 19.5% is required.

Additional Considerations for Storage Protection

Testing has shown that depending on the storage, oxygen levels as low as 11% is required for cartooned storage and 13% for plastic packaging. Also, the VdS 3527 test method, used for the design of these systems, is found to be not sufficiently conservative and hence, the design may not provide the required fire prevention for the storage.

Other factors needed to be accounted for in the system design are air at atmospheric conditions trapped in packaging or boxes, porous products with trapped atmospheric air, oxygen generating reactions and thermal runaway conditions observed in Lithium-ion batteries.

The insurance industry continues to have mixed views regarding the adoption of ORS technology especially where the atmosphere is normalised for maintenance, compromising the fire prevention properties, and formalised mitigation measures such as removal of storage or alternative fire detection, implemented.

Conclusions

ORS is a fire prevention system and it is important that the oxygen limiting concentration to prevent ignition, considers the worst credible fire scenario. Critical factors that need to be considered are ignition source strength and duration, stored commodity type, heights and moisture content.

Get in touch with us to discuss your plans if you are thinking about installing, or are currently installing, ORS systems.