Choosing the right clean agent for your fire hazard
Sprinkler systems are the most widely used form of fire suppression in the world. Their primary function is to preserve a building’s structural integrity long enough for people to evacuate, and for the fire department to arrive. Sprinklers perform this function very well, which explains why they have been the fundamental means of fire protection for nearly 150 years.
Unfortunately, sprinklers do little to preserve the contents of a building, and in fact, often contribute to the destruction of building contents, especially when those contents include sensitive electronics, paper archives or other valuable artifacts.
Halon was introduced as an ideal agent for solving this problem in the 1960s. It was non-conductive and it left no residue upon evaporating. But, halon was phased out of use in new extinguishing systems in the early 1990s because of its potential to deplete the ozone layer. Various different agents were introduced in the decades following the halon phase out. These agents are commonly referred to as “clean agents” and include HFC-227ea (also known by the Chemours™ brand of FM-200™), HFC-125 (also known by the Fike Corporation brand of ECARO-25®), FK-5-1-12 (also manufactured by 3M™ and sold under the brand of Novec™ 1230) and various inert gases, which include IG-55 (a 50/50 mix of argon and nitrogen), IG-541 (50/42/8 mix of nitrogen, argon and CO2), IG-100 (pure nitrogen) and IG-01 (pure argon).
While clean agents are recognized as the preferred means of protecting sensitive environments today, it can be difficult to know which agent to use in a given application. The chemical clean agents (HFC-227ea (FM-200™), HFC-125 (ECARO-25®) and FK-5-1-12 (Novec™ 1230), all extinguish a fire by the same mechanism (largely by heat absorption) and they all have the relative same degree of effectiveness.
Inert gases extinguish a fire by reducing the oxygen level down to a level where combustion cannot be sustained, typically around 12%. They all put out fires with equal effectiveness.
Given the relative parity among the chemical clean agents, and among the inert gases – when it comes to the ability to extinguish a fire – how does one decide which agent to use in a given application? As might be expected, the answer to this question is not simple. It depends on many different factors, and the relative importance of each factor to the end user. These factors include cost, environmental concerns, design flexibility, acceptance by local authorities, and a multitude of other factors that vary from buyer to buyer.
When cost is the primary concern, in most cases, a chemical agent system is going to be the least expensive option. Because inert gas systems work by reducing O2 levels to a point where combustion cannot be sustained, these systems must contain a volume of inert gas equal to about 40% of the volume of the protected space. Inert gas cylinders are high pressure cylinders and are available in a limited number of sizes and volumes, therefore, an inert gas system typically requires more cylinders than a chemical agent system. Chemical agent systems operate at much lower pressures than inert gas systems and therefore typically have a much larger range of available cylinder sizes. This results in an initial cost for an inert gas system that is usually higher than a chemical agent system. However, in the event of a system discharge, an inert gas system is less costly to refill.
Among the chemical agent systems, HFC-125 systems are the least expensive on an agent cost-per-pound basis. Because of its chemical properties (namely, its specific vapor volume – its propensity to expand and fill a space) you need 10% less HFC-125 to protect a given volume than would be needed if that same space were protected with HFC-227ea. When compared to FK-5-1-12, the difference is even more dramatic, with 30% less agent being required with an HFC-125 system. This lower cost-per-pound, combined with fewer pounds of agent needed to protect a space, make HFC-125 the low-cost clean agent option. HFC-227ea is the next lowest cost option, and FK-5-1-12 is typically going to be the most costly clean agent option. However, cost isn’t always the overriding factor when choosing a clean agent system.
Halon was phased out nearly 30 years ago due to its ozone-depleting potential. The past decade has seen growing concern over global warming potential (GWP) of fire suppression agents. CO2 is used as the reference point in measuring global warming potential, and is assigned a value of one. The halocarbon agents used in fire suppression (such as HFC-125 and HFC-227ea) have GWPs of around 3,000. FK-5-1-12 has a global warming potential of one. When environmental concerns outweigh cost concerns, this makes FK-5-1-12 an attractive clean agent option. Inert gases, such as nitrogen and argon, have no global warming potential. And, because they are extracted from the atmosphere to begin with, are environmentally benign, making inert gas the greenest clean agent option.
Inert gas systems, while usually more costly to purchase and install than chemical agent systems, offer the greatest design flexibility. This is largely a function of two variables: 1) Inert gas is stored in cylinders at pressures exceeding 4,000 psi, vs. chemical agents which are stored at 360 psi to 725 psi, and 2) Inert gas is stored as a gas, vs. chemical agents which are stored as a liquid.
Higher pressures and single phase, gaseous flow through the fire suppression system pipe network, mean that inert gas systems have more energy upon discharge and lower friction losses than chemical agents. Upon discharge, chemical agents exit the container as a liquid. Liquid flow encounters more friction loss than gas flow. Additionally, energy is lost as the liquid flowing through the pipe changes phase and becomes a gas. All of this adds up to shorter pipe runs, and larger diameter pipe for chemical agent systems.
Inert gas is stored as a gas and discharged as a gas. It therefore does not lose energy to phase change and encounters lower friction losses. This allows inert gas systems to flow longer distances through smaller diameter pipe. It also allows for more flexibility when it comes to using a central bank of cylinders to protect multiple hazards. The cylinder bank can be located well away from the protected hazard or hazards, and can even protect hazards located many floors apart in a multi-story facility. These greater flow distances make inert gas an ideal agent for protecting a range of hazards at industrial facilities with a single bank of cylinders.
Acceptance by Local Authorities
All of the clean agent systems are approved by the major international fire protection standards agencies and environmental policy agencies. Among the chemical agents, HFC-227ea has the longest-standing track record and the greatest number of installations. It is by far, the most globally specified chemical agent. Inert gases are also accepted worldwide, primarily because of their favorable environmental profile and long history of use in fire suppression. Where ease of approval by national and local agencies is the primary concern, this makes HFC-227ea and inert gas the agents of choice.
Clean agent fire suppression systems are the clear choice for protecting mission critical assets that are susceptible to damage by a fire sprinkler system. Multiple agents have been introduced in the decades following the halon phase out and each of those agents offers a unique set of benefits. The variety of clean agent systems available today ensures that there’s a system suitable for virtually any combination of applications and customer priorities. Many fire suppression system manufacturers offer both an inert gas and a chemical agent option. Others, like Fike Corporation, have taken the approach of offering the full range of every internationally accepted chemical and inert gas agent. This ensures that the buyer of a fire suppression system purchases a system that meets the exacting requirements of the particular fire hazard being addressed, and meets the buyer’s cost, environmental and design requirements.
For more information, go to www.fike.com