Life After Halon

11/01/2005


The halon phase-out is on, and has been for quite some time. In today's increasingly environmentally sensitive construction world, the not-so-environmentally friendly fire-suppression method is becoming obsolete.

Replacement of halogenated agent suppression systems first became a concern of physical plant managers and fire suppression designers with the adoption of the 1987 Montreal Protocol—amended in 1990 and 1992—wherein member states agreed to work toward reducing ozone-depleting chemicals. The requirements of the protocol created a surge of research, development and marketing of new alternative suppression agents. The years that followed led to an inevitable shakeout of suppression agents in the marketplace and some standardization of the engineered delivery systems for these agents.

Predictably, the issue has taken on greater immediacy as the original halon systems age and the halon agents to refill these systems become less available. Facilities with areas protected by halon systems must decide whether or not these should be replaced by alternative clean agent suppression systems. By the way, the term "clean" comes from the fact that use of these agents results in minimal damage to the environment. To make an informed determination as to whether or not the expense of clean agent suppression can be justified, all of the following questions must be considered:

  • Why is—or what in—the hazard area is mission-critical?

  • What compliance with codes/standards/design criteria is required?

  • What are the architectural/mechanical characteristics of the hazard area?

  • What suppression product is best suited for the hazard area?

  • How should the system be engineered, procured and installed?

Before addressing these questions, however, some background information must be obtained, including some basics of fire science, descriptions of suppression methods and some history of the uses of halon and clean agents. Empowered with this fundamental understanding, the issues that will affect clean agent system selection and design should come into better focus.

Suppression 101

As the early research into halons developed, the accepted models of the combustion process underwent a fundamental change. Fire theory in the first half of the 20th century was based upon a "fire triangle" in which fuel, oxygen and heat were the essential elements for combustion.

As the mechanics of halon suppression became better understood, a fourth combustion component was identified. The presence of an "uninhibited chain reaction" is also necessary to sustain combustion and it is this chain reaction that is disrupted by the chemical structure of the halon and many of the newer clean agents. However, some clean agents extinguish by reducing the oxygen level at the fire. In essence, a three-dimensional "fire tetrahedron" replaced the original triangle.

Knowledge of the "classification" of fires is also critical to understanding the correct application of clean agents:

  • Class A: ordinary combustibles

  • Class B: flammable liquids

  • Class C: electrical equipment

  • Class D: combustible metals

The Class A and D fuel loads can support a deep-seated fire, i.e., combustion that is not on the exposed surface of the fuel load. As clean agents don't penetrate well to the deep location of the combustion reaction, they are less effective on Class A and Class D deep-seated fires. Conversely, Class B and C fires tend to burn primarily on the surface and the agent is therefore quite effective on these types of fires.

When the agent is applied, the physical properties of the chemical and the previously discussed mechanism of suppression result in the agents' clean character. Most clean agents are stored as either a liquid or gas under pressure and discharged as a vapor to the fire. As the components of the agent react to extinguish the fire, it decomposes into trace amounts of inert and—by design—non-toxic products. Even though the vapor of the undecomposed agent is typically heavier than air, the vapor still ventilates rapidly and well with any movement of air out of the hazard area. As a result, the agents leave little or no residue that is corrosive or conducts electricity.

To adequately discuss design considerations for clean agent suppression systems, some basic information about the available agents is handy. Table 1 (below) lists some of the historical halons, current clean agent alternatives, some water-based alternatives and several characteristics of these systems.

How necessary?

Facilities with an existing hazard area halon system are currently faced with three options:

  • Determine that the halon system, or any other clean agent system, is not necessary and have the system removed.

  • Attempt to maintain the halon system until circumstances require its removal or replacement.

  • Replace the halon system with another clean agent suppression system.

Even though these options are conceptually straightforward, the process of selecting an option and its consequences are not simple or inexpensive. Therefore, before committing to the expense of the design, installation and maintenance of either the second or third option listed above, facility management should determine that the hazard area indeed needs a clean agent system.

The primary justifications for a clean agent system are:

  • The outside agencies or applicable codes require it.

  • The cost of the contents of the hazard area due to fire, or the cost of loss of use of those contents due to fire, will exceed the cost of the system.

  • Operations in the hazard areas are mission-critical and shut-down time must be maintained to a minimum.

Note that one common, primary justification for a clean agent system is conspicuously absent. The possibility of damage from an accidental water sprinkler release should not be the primary reason for installation of a clean agent system. That being said, accidental release concerns may certainly be a secondary consideration. If, however, damage from an accidental water release is the primary concern, there exist other solutions that are less expensive than clean agent systems. These include, but are not limited to, pre-action systems, water-mist systems and hazard-specific suppression equipment.

Another myth is that all data processing centers must have clean agent suppression. This was largely true in the day of the high-dollar mainframe computer. Now, however, distributed servers, remote backup systems, decreased hardware prices and increased off-the-shelf availability means that many of today's data processing rooms may not need the expense and maintenance efforts that accompany clean agent systems. Each center should be evaluated for its replacement costs and mission criticality before automatically installing agent suppression.

Outside agencies

As mentioned at the start of this article, outside agencies—the governments ascribing to the 1987 Montreal Protocol—prescribed the replacement of halon systems. When considering the requirements for installation of clean agent systems, an outside agency can be any party that, through its relationship to the facility, can compel installation of a system. Obviously, government agencies with jurisdiction over the facility may require a system installation. These agencies can be at local, state or federal levels and include not only those with responsibility for general enforcement of adopted codes, such as local fire prevention departments, but also governmental bodies assigned specific tasks that include standardizing facility safety (e.g., aircraft control facilities and the Federal Aviation Administration).

Non-governmental outside "agencies" include insurance provider conditions, the policies of the facility's corporate parent, "trade" or "brand" affiliation agreements and even requirements dictated by a facility's clientele.

Applicable codes that carry the force of law can require the installation of clean agent systems. Among all the national codes that are often adopted, however, there are only a few occasions where they mandate installation of clean agent systems. Some commonly adopted codes that require installation of systems include the International Building Code, International Fire Code and NFPA 101, Life Safety Code.

Of more significance are the several standards that specify compliance requirements for installation and performance of clean agent systems, including NFPA 75, Protection of IT Equipment; NFPA 2001, Clean Agents; UL 555, Dampers; and NFPA 70, National Electrical Code. These codes and standards are among the most frequently used standards. They not only provide guidelines that must be considered during design and installation, but also list the mandatory requirements for clean agent systems that apply whether the system is mandated or elective.

Finally, additional compliance requirements apply to other building systems that are affected by, that interact with, or that are connected to the clean agent systems. These standards include, but are not limited to, NFPA 13, Automatic Sprinklers; NFPA 72, National Fire Alarm Code; and NFPA 76, Telecom Facilities.

When deciding whether to install a clean agent system, the facility's management and design team must consider the bona fide interests of all relevant outside agencies. Additionally, if a clean agent system is determined to be required or desirable, the applicable codes and standards must be researched and implemented as is appropriate.

Design and cost considerations

Once a clean agent suppression system is determined to be necessary, the cost issues become one of the two subjective factors that affect selection of the type of agent and system. The second is consideration of specific agent characteristics, which will be discussed in the next section. The challenge comes in identifying all of the costs that occur during the engineered life of the new systems. There are expenses associated with "hanging on" to the existing halon systems for the transition interim. These should be added to the costs calculated for demolition, engineering, installation, recharging after discharge and maintenance of a new agent system. Some general comparisons of direct cost of design, controls, piping and suppression agent for "apples to apples" systems is shown in Table 2 (below).

Installation of the system will include many indirect costs that can vary widely in amount depending upon the specifics for each individual system. Among these are costs for engineering evaluations to select design criteria and agents; air-handling and architectural modifications necessary to maintain levels of agent in the hazard areas; systems to exhaust the agent; and modifications to building automation and electronic systems to provide reliable detection and control functions. With regard to electronic detection and control, a specialized fire alarm control unit listed for releasing-agent duty is employed. This control panel, together with its peripheral input and output devices, is designed to permit customized detection, release and notification sequences of operation.

Furthermore, each installation will have unique impact and transition costs associated with the operations affected by the work in the hazard area. Different agents and designs will affect these impact and transition costs, so design professionals, facility managers and operations management must all be involved in selecting the suppression agent system design.

Other considerations

Historically, halons have been subjected to scrutiny as to their toxicity, environmental impact and effectiveness. As the new alternatives have been introduced, they also have been subjected to similar scrutiny. Table 3 (below) summarizes the effects of these newer agents and indicates that there are only marginal differences in the effects of these products. Indeed, with the exception of the environmental concerns, there is little difference between these agents and halon 1301. These differences, though small, should still be considered for their effect on the application of the new suppression system.

The end is near

As existing stockpiles of halons are depleted and destroyed, halon-based suppression systems will be removed or replaced. Facilities that have not prepared for the transition to newer agents risk finding themselves confronted with a system replacement that is the result of an unplanned incident instead of a budgeted and structured process.

Hopefully, facilities will educate themselves as to the complexity of and potential for expensive missteps that may result in a hastily implemented system replacement. Removal of the halon systems, if completed as a planned and carefully developed project, will eliminate the need for replacement where systems are determined not to be necessary—and assure that those installed are well engineered for their mission.

Table 1

Agent

Mode

Comments

Halon 104

Extinguishes by inhibiting combustion reaction.

First halon agent, carbon tetrachloride, discontinued due to toxicity.

Halon 1301

Extinguishes by inhibiting combustion reaction.

Gained popularity in 1960s for protection of data processing equipment. Resulted in first NFPA Installation Standard. Still common.

Carbon Dioxide (CO 2 )

Extinguishes by reducing the oxygen level.

Requires large concentration on the fire for effectiveness.

Inergen

Extinguishes by reducing the oxygen level.

Combination of inert gases. N 2 ArCO 2 .

FE-227 ea

Extinguishes by inhibiting combustion reaction.

Also known as FM-200. Widely accepted.

Novec 1230

Extinguishes by inhibiting combustion reaction. Coat Surface.

New agent.


Table 2
Installation Comparison (400 sq. ft. with 10-ft. Ceiling)

Agent

Inergen

FM 200

Novec 1230

Agent Quantity

196 cu. ft. (1-439-cu.-ft. cylinders)

140 lbs. (1-200-lb. cylinder)

152 lbs. (1-280-lb. cylinder)

Cylinder Space

6%%MDASSML%%10 sq. ft.

3%%MDASSML%%5 sq. ft.

3%%MDASSML%%5 sq. ft.

Cylinder/Nozzle Locations

Flexible

Critical: outside but adjacent to protected area

Flexible within limits

Vendors

Single vendor

Multiple installers/distributors

Multiple installers/distributors

Other Factors

Small nominal piping diameters

Limited nozzle and piping configurations

Limited nozzle and piping configurations


Table 3

Inergen

FM 200

Novec 1230

Effect on Occupant

Reduced oxygen level is not harmful when limited to 5-min. exposure. Frostbite possible if too close to nozzle.

Increases heart and breathing rates (when used as medical gas propellant). May aggravate exisiting cardiac or respiratory conditions. Frostbite possible if too close to nozzle.

Increases heart and breathing rates. May aggravate existing cardiac or respiratory conditions. Frostbite possible if too close to nozzle.

Environmental Effects

No ozone depletion. Low CO 2 discharge.

No ozone depletion. 35-year atmospheric life.

No ozone depletion. 5-year atmospheric life.

Clean-up

Ventilate, no residue.

Ventilate, no residue.

Ventilate, some residue, containment and disposal of residue.






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