Data centres are ‘mission critical’ facilities used to house computer systems, telecommunications and storage systems for large multinational organisations. They consume vast amounts of electricity and must have continuous power supply 24 hours a day, 365 days a year. What is less known are the potential major safety issues in data centres. Ireland is already home to a significant number of global data centres belonging to the tech giants. Richard Coffey, a senior EHS consultant with PM Group, reviews the key safety issues.

Overview of main hazards

A typical conceptual layout for a data centre is given in Fig. 1. A data centre consists of equipment room(s), utilities, and support infrastructure. The main process-related hazards in data centres are as follows: 1.) Fuel oil storage and handling 2.) Battery charging activities 3.) Hazardous treatment chemicals 4.) Fire suppression gases 5.) Arc flash hazards These hazards are reviewed in the following sections.

Emergency generators

Diesel generators are frequently used to provide emergency back-up power in the event of a major grid outage. Data centres can have many banks of diesel generators, which are housed in a separate area. Together, they are designed to produce power that is sufficient to cover the data centre’s electricity demand in an emergency. Bulk diesel is usually stored at ambient conditions in bulk storage tanks. The ambient conditions mean that hazardous vapours are not expected to arise inside the headspace of the tanks. The maximum ambient design temperature in Ireland is 30°C, which is more than 15°C below the flash point. The basis of safety is the prevention of explosive atmospheres by storing the fuel oil externally at ambient temperatures. Diesel generators burn approximately 50 per cent (the exact fraction may vary from this) of the fuel that is supplied to it. The unused fuel is returned from the generators at a raised temperature. However, the temperature of diesel within the circuits can gradually increase over a prolonged period of operation. Fuel temperature monitoring and fuel coolers are therefore required to control the diesel temperature within the circuits to avoid potentially explosive atmospheres. The need for a smarter solution for emergency power supply has led to the advent of modern gas-fired engines which have lower emissions than diesel engines and have been reported to work faster. Gas engines also have no requirement for fuel storage.

Battery rooms

Within data centres, block batteries ensure that all operating applications can run for a limited period of time. This backup system makes it possible to provide power from the time a utility company experiences a total blackout to the time that the diesel generators start up. Battery charging can give rise to hydrogen gas generation and potentially explosive atmospheres. The strategies for managing these hazards usually involve good ventilation. Among the innovative approaches in large server halls is low energy-efficient ventilation during normal operation and the use of hydrogen monitoring to ramp up ventilation in the event of hydrogen detection. IEC 62485-2:2010 discusses provisions to protect against explosion hazards for stationary batteries. The standard presents calculations on ‘safety distances’ for that area in the immediate vicinity of the batteries being charged where ventilation can be reduced and where non-sparking or ATEX rated electrical equipment is required. The basis of safety for locations where battery charging takes place is the prevention of flammable atmospheres by the use of adequate ventilation. From IEC 62485-2:2010, the minimum air flow rate for ventilation of a battery location or compartment is given by the following formula: Q = 0.05 x n x Igas x Crt x 10-3 [m3/h] n = number of cells per battery Igas = current producing gas in mA per Ah Crt = capacity C10 for lead acid cells (Ah) Ventilation systems should be designed with adequate redundancy. If duty fans fail, then spare fans should be considered in the design. N+1 redundancy is commonly applied in conjunction with hydrogen detection. In recent years, lithium-ion batteries are making inroads. Although more costly, they have life spans significantly greater than that of the traditional valve-regulated lead-acid batteries. This translates into fewer battery replacement cycles and fewer operational disruptions. While the costs continue to decrease, manufacturers hope to sell the advantages of lithium-ion batteries, including a higher power density, which means less space for the same amount of power.

Fire suppression systems

Fire suppression flooding systems are often used for Information Technology Equipment (ITE) areas. Suppression gases fall into two categories: inert gases and chemical agents. The power to all electronic equipment should be disconnected upon activation of a gaseous agent total flooding system. Gaseous agent systems shall be automatically actuated by an approved method of detection meeting the requirements of NFPA 72 and a listed releasing device compatible with the system. [caption id="attachment_45387" align="alignright" width="300"] Fig 3 Fire suppression systems[/caption] Where the operation of the air-handling system would exhaust the agent supply, the air handling system is usually interlocked to shut down when the extinguishing system is actuated. Alarms are provided to give a positive warning of a pending discharge and an actual discharge. A risk assessment may be required to ascertain if oxygen depletion monitoring is required in the event of activating a gaseous flooding system. This is because the gaseous suppression gases often use inert gases and the extent of flooding of the room areas may deplete oxygen levels to such an extent that asphyxiation hazards arise should fire-fighting personnel enter the area. In these scenarios, they should always wear appropriate breathing apparatus before entering.


A range of treatment chemicals are often used in data centres for the treatment of cooling water and similar systems. These chemicals can include: 1.) Corrosives (for example, sulphuric acid) 2.) Oxidising (for example, Sodium Hypochlorite) A well-recognised guide on chemical storage is given in the UK HSG71 'Chemical warehousing: The storage of packaged dangerous substances'. This guidance covers the storage of chemicals in drums, IBCs and tanks. With regard to storage, a key issue is the consequences of incompatible materials being stored too close to each other, resulting in a fire or explosion. Such an event can result in dangers to operators on site and environmental and safety hazards. For example, a fire can lead to large volumes of contaminated fire water and the escalation of the consequences due to the hazardous properties of the chemical substances.

Arc flash

Data centres operate at voltage levels where they must use a series of mechanisms to 'transform' or 'step down' power from the incoming high voltage supply at which it is received. Unfortunately, a small amount of energy gets lost as waste during this step. One way to reduce such waste is for data centres to operate at as high a voltage level as feasible. As they do so, however, it is important to examine the potential safety implications, including the heightened risks associated with arc flash incidents. [caption id="attachment_45388" align="alignright" width="200"] Fig 4 Arc flash hazards require PPE[/caption] All switchgear should conform to international standards such as IEC 61439 and be internally arc flash assessed. The results of these calculations enable managers to specify the personal protective equipment (PPE) required to address the established risk levels. Building in engineering controls to help mitigate such risks from the start can mean the difference between a 'survivable injury' and no injury at all. For example, with arc-resistant switchgear, workers may be permitted in front and around the perimeter of switchgear with designated PPE. Passive arc-resistant switchgear can still cause enough internal equipment damage to require significant repair or replacement. However, newer, more active designs incorporate fast-acting switches that can extinguish arcing faults in as little as ¼ cycle, reducing the risk to both equipment and personnel. Building data centres with explicit consideration for reducing arc flash risks can help boost both safety and uptime. One important first step is to undertake an arc flash analysis before the design is substantially complete, rather than waiting until switchgear and other electrical equipment arrives on site for installation.

Safety culture

A final safety challenge which is important to mention can be the ‘safety culture’. ‘Uptime’ and energy efficiency have traditionally been the two main Key Performance Indicator (KPIs) for data centres. However, as we have discussed, these facilities can present a range of significant safety hazards. The sheer scale of today’s data centres has amplified these hazards. [caption id="attachment_45389" align="alignright" width="300"] Fig 5 PM Group safety focus[/caption] From PM Group’s international experience, safety must be adopted as a business KPI to secure the fast growth and sustainable development of data centres. Safety is not optional; it is an important measure of business performance.


While they may appear quiet and harmless on the outside, data centres use vast amounts of electrical energy and present many safety hazards. These range from fuel oil storage and battery charging risks to the use of hazardous treatment chemicals. Their scale of operations and the emphasis on uninterruptible operation has presented designers and operators with challenges. These challenges are best managed by adopting safety as a KPI both in design and during operations. Author: Richard Coffey, CEng MIEI, is a senior consultant in the Environmental Health & Safety Department of PM Group. PM Group is an engineering and construction management company with clients from the biopharma, food, energy and healthcare sectors. The group is headquartered in Ireland and has operations in the UK, Poland, Singapore, India and the US