Managing the risks of fire or explosion

Published: 6-Sep-2013

Use of high-risk substances and processes in cleanrooms means mitigating hazards such as fire and explosion. Duri Barblan, Siemens Building Technologies, considers the safety issues and offers some solutions

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For contamination-sensitive products, the cleanroom is at the heart of production. Dust, micro-organisms or smoke can all adversely affect sensitive production processes and product quality. Ensuring personal safety is also a major challenge. Active agents in pharmaceutical production facilities, dangerous pathogens in a security lab, flammable cleaning substances and toxic chemicals in a semiconductor plant are all fundamental safety risks for staff and the environment. Although potentially dangerous, they are nevertheless unavoidable components within the processes and, as such, must be reliably brought under control.

It is widely acknowledged that safety is never absolute. According to a generally accepted definition (ISO/IEC Guide 51:1999), safety is the absence of unacceptable risk. Consequently, companies and organisations must identify and evaluate all potential risks, as well as define and continuously review the levels of acceptance.

The ISO 31000:2009 standard provides the necessary methods for managing all possible risks. Project-specific sources of danger can be determined by analysing and evaluating the risks. These risks can be managed with a sufficient combination of organisational (e.g. processes training), structural (room and facility structures) and technical measures. Due to high-risk substances and processes or the most stringent quality standards, cleanroom environments, in particular, must meet extremely strict requirements when it comes to personal safety and product and environmental protection, as illustrated by the following examples.

Effective explosion prevention: Gases and solvent vapours can produce a dangerous explosive atmosphere due to their significant potential for ignition. Special installations and specific fire and gas detection solutions are required in these explosion-hazardous areas to alleviate such risks, as well as for controlling, regulating and monitoring the HVAC systems and process equipment.

A gas detection system must reliably detect the anticipated flammable gases before the minimum explosion limit is reached, and it must alert people, display the location of the danger and take action to prevent fire or explosions.

Fire safety: A fire in a cleanroom is the single greatest risk. Short-circuits, spontaneous ignition or leaks in containers of highly flammable or self-igniting fluids or gases are typical causes of fire. Damage to equipment and installations resulting from fire can generate consequential losses of millions of dollars within minutes. Even small fires can cause considerable damage.

Once a fire is detected, safety shutdown procedures are usually triggered automatically. This has a significant impact, particularly in cleanrooms, since shutting down ventilation systems and closing fire dampers means that the pressure cascades can no longer be maintained, which can cause uncontrolled cross-contamination in the rooms. Products can no longer be used and under certain circumstances toxic substances may escape from controlled zones. It may be several days before a cleanroom can be placed back into active operation – for example, for sterile production. A fire detector that triggers a false alarm has serious potential consequences similar to those of a real fire. Experts therefore advise maintaining a high level of safety in cleanrooms. Preventive and active fire safety measures are particularly important.

Reliable fire detection: The reliability of an alarm in detecting genuine fire incidents rather than generating false alarms, along with the amount of time that passes between the outbreak and detection of a fire, are key to a reliable fire safety strategy. Rapid early detection minimises process interruptions and avoids secondary damage.

Cleanrooms need to have high air exchange rates, rapid air velocities and directed airflows to minimise particle concentration. Particles are flushed away with clean air. However, a consequence of this approach is that it is much more difficult to detect a fire, since these high airflows mean that ceiling-mounted fire detectors are susceptible to detecting the fire at a much later stage, often at a point when damage has already occurred. Reliability and early detection can, though, be increased.

High airflows mean that ceiling-mounted fire detectors are susceptible to detecting the fire at a much later stage

Fire detectors can be provided with special cleanroom parameter sets that are designed specifically for clean environments. Additionally, to detect smoke at a very early stage, room air samples are actively extracted at suitable points in the cleanroom. These samples are analysed to distinguish reliably between smoke, dust and steam particles.

Once a real fire hazard has been detected, it is critical to take immediate action tailored to the situation. Modern and efficient cleanroom solutions therefore integrate fire detection, voice alarms and extinguishing systems. This allows direct interactions and enables the person in the control room to monitor alarms, events and system malfunctions, as well as to operate all systems uniformly in real time.

Efficient extinguishing: The substances used in cleanrooms create specific risks that influence the choice of a suitable extinguishing solution. Water cannot always be used as the extinguishing agent and, even if it is, special measures must be adopted; for example, to reliably collect contaminated water once it has been deployed in the extinguishing process.

Protecting room contents

Protecting cleanrooms is a major challenge due to their impermeability, complex air circulation patterns and the necessary pressure cascades. The high risk of fire, combined with the significant value of certain equipment, means that object protection is the most commonly employed extinguishing solution. Safety cabinets (barrier isolators), for example, are provided with an autonomous object extinguishing system to monitor critical zones separately and to immediately trigger extinguishing in an emergency.

Inert gases are preferred for this purpose. These gases are chemically neutral and generate no reaction products when the extinguishing agent comes into contact with the fire. This means that the extinguishing agent does not damage or contaminate the equipment or goods produced – a clear advantage in protecting cleanrooms. Certain inert gases such as nitrogen and argon are also non-toxic, colourless, odourless and tasteless, which is especially important in the pharmaceutical and food and beverage industries.

Safety cabinets are often provided with an autonomous object extinguishing system to monitor critical zones separately

Safety cabinets are often provided with an autonomous object extinguishing system to monitor critical zones separately

Orderly evacuation: If a particular danger is detected, such as a fire, it may require immediate evacuation of the building or the threatened areas. Once again, cleanrooms present special challenges, since it is important not to release toxic substances during evacuation. It may also not be possible to effectively extract these substances. Due to these specific requirements, voice evacuation systems are an effective solution. They use visual and acoustic signals, as well as spoken language, to inform personnel of the current situation, transmitting clear instructions to the cleanrooms and detailing the correct action to be taken. This guarantees the safe and orderly evacuation of the cleanroom and adjacent areas. Additional safety warnings and clear instructions can also prevent contamination caused by the arrival of investigation or fire fighting teams.

Protecting employees, product quality and the environment are fundamentally dependent on the environmental conditions. Cleanroom environments require the best technical protection strategies without compromising product protection and personal safety. Only those companies that reliably protect their employees and assets can ensure long-term safety and successful production.

Cleanroom environments require the best technical protection strategies without compromising product protection and personal safety

Comprehensive cleanroom solutions integrate all the building systems for regulating, controlling and monitoring cleanrooms. In doing so, they minimise risks over the long term, increase efficiency and ensure verifiable conformity with the applicable regulations. This approach maximises safety and ensures high system synergies that continue to pay off year after year.

Single-source solutions: A comprehensive safety concept can help maintain a reasonable level of safety. The Siemens Building Technologies Division offers this type of concept from a single source: comprehensive fire and gas detection, specific extinguishing solutions for room and object protection, extensive experience with explosion-hazardous areas and additional safety through innovative voice evacuation, to name just a few examples. Additional safety systems such as video surveillance and access control equipment can further enhance cleanroom protection.

The Siemens cleanroom solution is based on proven and qualified elements for GMP-compliant environmental conditions, from room pressure regulation and interlock control to comprehensive monitoring of all GMP-critical parameters. Drawing on a wealth of experience from more than 2,000 completed cleanroom projects, the company can support individual projects from the concept phase to shutdown.

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