Chapter 7: SEARCH FOR NEW FIRE J. Douglas Mather, Ph.D. SUPPRESSANT CHEMICALS Chemical Development Studies, Inc. Robert E. Tapscott, Ph.D. GlobeTech, Inc. TABLE OF CONTENTS 7.1 Fire Suppressant Replacement Knowledge Prior to the NGP .........................................612 7.1.1 Overview of Early Halon Replacement Efforts ....................................................612 7.1.2 Fire Suppressant Research – 1974 Through 1993.................................................613 7.1.3 DoD Technology Development Plan (1993 to 1997)............................................615 7.1.4 Advanced Agent Working Group (AAWG) .........................................................616 7.1.5 Summary: Alternative Agents and Selection Criteria Prior to the NGP ...............622 7.2 The NGP Approach to New Chemicals Screening..........................................................612 7.3 NGP Surveys of Inorganic Chemical Families................................................................612 7.3.1 Main Group Elements - Group I............................................................................626 7.3.2 Main Group Elements - Group II ..........................................................................627 7.3.3 Main Group Elements - Group III.........................................................................627 7.3.4 Main Group Elements - Group IV.........................................................................628 7.3.5 Main Group Elements - Group V..........................................................................634 7.3.6 Main Group Elements - Group VI.........................................................................645 7.3.7 Main Group Elements - Group VIII (Noble Gases) ..............................................646 7.3.8 Transition Metal Based Compounds .....................................................................646 7.3.9 Inorganic Chemicals - Conclusions.......................................................................647 7.4 NGP Surveys of Organic Compounds .............................................................................647 7.4.1 Highly Efficient Thermal Agents..........................................................................647 7.4.2 Tropodegradable Candidate Compounds ..............................................................658 7.4.3 Bromofluoroalkenes ..............................................................................................662 7.4.4 Fluoroalkoxide and Fluoroalkyl Phosphorus Compounds ....................................665 7.4.5 Fluoroalkyl Nitrogen-based Candidates................................................................680 7.4.6 Bromofluoroalkyl Nitrogen-based Candidates......................................................685 7.4.7 Fluorinated Ethers .................................................................................................687 7.4.8 Bromofluoroethers.................................................................................................691 7.4.9 Bromofluorooxiranes.............................................................................................694 7.4.10 Bromofluoro / Fluorinated Aldehydes and Ketones..............................................695 7.4.11 Bromofluoro Alcohols...........................................................................................695 7.4.12 Iodinated Hydrocarbons ........................................................................................696 7.5 Chemical Family Options and Replacement Issues.........................................................700 7.5.1 Suppressant Criteria and Selection Constraints.....................................................700 7.5.2 General Conclusions..............................................................................................701 7.6 References........................................................................................................................702 612 Search for New Fire Suppressant Chemicals 7.1 FIRE SUPPRESSANT REPLACEMENT KNOWLEDGE PRIOR TO THE NGP 7.1.1 Overview of Early Halon Replacement Efforts As described in Chapter 1 of this book, in the years following the Army-Purdue study, there was extensive scientific and engineering research that led to the commercialization and widespread use of halon 1301. Following the adoption of the Montreal Protocol on Substances That Deplete the Ozone Layer in 1987, organized efforts to identify replacements were initiated by a broad range of governmental and non-governmental groups. These efforts were hastened in the United States by the planned phase-out of production of halon 1301 (CF3Br) and halon 1211 (CF2ClBr) by the end of 1993. The replacement of halon 1301 presented some daunting challenges. Halon 1301 is unique as a brominated halocarbon. Its -58 °C boiling point is the lowest of the bromofluoroalkane chemical family, and its toxicity is quite low. It is an efficient fire suppressant and explosion inertant. It has great dimensionality (space filling), high tolerance to less than optimal discharge technique, and excellent chemical stability. Early results showed that a small change in the molecule could lead to large and conflicting effects on key performance properties. For example, the replacement of a fluorine atom by a hydrogen atom to produce halon 1201 (CF2HBr) reduced the estimated atmospheric lifetime from 65 years to 15 years, but raised the boiling point to -15 °C. Nonetheless, the search for alternatives to the firefighting halons began as a quest for a "drop-in," a chemical that would fit into existing fire suppression systems and perform just like or better than the halon it was replacing. During the early years of this research, there were frequent changes in thinking among those involved in identifying new chemicals. For instance, it was realized that instead of a single drop-in replacement being identified for halon 1301 (as well as halon 1211) the world of fire suppression applications was going to see a broad range of new agents and technologies. Furthermore, the criteria for environmental acceptability changed. With the emphasis on dramatic reductions in both stratospheric ozone depletion effects and atmospheric global warming potentials, the research focus shifted to identifying short atmospheric lifetime molecules. These compounds incorporate structural components that are reactive with atmospheric constituents of the atmosphere or are photochemically reactive, as shown in Table 7–1. Table 7–1. Tropospheric Removal Mechanisms. Primary Removal Mechanism Example Families Photodegradation Iodides, carbonyls, bromides Reaction with hydroxyl radicals Alkenes, aromatics, hydrogen-containing amines, hydrogen- containing ethers, carbonyls Physical removal Ketones, alcohols, esters Reaction with tropospheric ozone Alkenes Risk assessment based toxicity tests and limits were identified, and understanding of situational toxicological constraints underwent considerable evolution. Some chemical options considered for halon replacement (e.g., the perfluorocarbons) were at first embraced, but later discarded as understanding of global warming impact issues developed. By the time NGP research began in 1997, these efforts had resulted in the birth of new fire extinguishment technologies, a broader view of the chemical options available, and emerging Fire Suppressant Replacement Knowledge Prior to the NGP 613 understanding of the dynamics of fire suppression under the adverse conditions encountered during the suppression of in-flight fires in aircraft. The following is a brief summary of these activities and their outcomes. 7.1.2 Fire Suppressant Research - 1974 Through 1993 Scientists at the Naval Research Laboratory had begun investigation of the principles of fire suppression by halon 1301 as early as 1974. This was driven by the Naval Air System Command's desire for a more efficient agent for suppressing in-flight fires. The outcome of this and the few contemporary efforts are summarized in Reference 1. As Rowland and Molina's finding that such compounds could deplete stratospheric ozone became well-known, this research broadened to a variety of fire suppression related 2,3 4,5 topics and potential chemical agents. Research at NRL also studied CF3I flame extinguishment and conducted studies of hydrogen fluoride (HF) byproduct formation resulting from halon 1301 fire extinguishment.6,7 Beginning in the mid-1980s, the U.S. Air Force (USAF) sponsored research at the New Mexico Engineering Research Institute (NMERI) on “first generation” halon replacement candidates focused on chemicals that were or soon would be readily available and that had a significant amount of known toxicological information.8 This strategy was adopted for two reasons: 1. Available chemicals could be tested at relatively low cost to determine effectiveness in firefighting scenarios, and 2. Toxicological testing of candidates was expensive and time consuming. Chemicals developed primarily as chlorofluorocarbon (CFC) replacements were the major focus as first- generation replacements. Relatively large quantities of these chemicals were available, and manufacturers were supporting toxicological testing, as these chemicals were often being considered for applications as refrigerants, solvents, and foam blowing agents, in addition to fire suppression. This strategy proved successful in that a number of halon replacement candidates were identified that were readily available for testing that had a significant amount of toxicity