Halon Replacements: An Overview - ACS Symposium Series (ACS

Chapter 1

Halon Replacements: 1

An Overview 2

Andrzej W. Miziolek , Wing Tsang , and John T. Herron

2

1

U.S. Army Research Laboratory, A M S R L - W T - P C , Aberdeen Proving Ground, MD 21005-5066 Chemical Science and Technology Laboratory, Chemical Kinetics and Thermodynamics Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-0001

Downloaded by 80.82.77.83 on September 19, 2017 | http://pubs.acs.org Publication Date: May 5, 1997 | doi: 10.1021/bk-1995-0611.ch001

2

In 1975 a book was published t i t l e d Halogenated Fire Suppressants [1] as an ACS Symposium Series monograph. That book was edited by Richard G. Gann, then at the Naval Research Laboratory, and reflected much of the content of a symposium held that year on the same topic in San Antonio, Texas. The monograph contained 15 chapters which were concentrated largely on mechanistic studies of flame inhibition and extinguishment using Halon 1301 (CF Br) as well as a few other brominated compounds. The objective of the symposium was to answer the question of whether Halon 1301 was indeed the best compound for f i r e suppression effectiveness. R.G. Gann started the preface of that book with the quotes: "In many areas of the f i r e problem, proposed solutions rest on limited experience, shaky assumptions, and guesswork." [2] and "More research is needed on extinguishing agents..., to improve the effective ness of existing agents and to investigate the chemical and physical mechanisms of new agents." [2] Judging from the content of t h i s , now second book on the subject of f i r e suppression agents, one can conclude that although much progress has been made in understanding chemical and physical mechanisms of f i r e extinguishment, we certainly are not there yet. 3

When the f i r s t book was published, the issue of stratospher ic ozone depletion had just been raised with the initial emphasis being placed on chlorofluorocarbons (CFCs) as the class of compounds of immediate concern. In due time, i t was recognized that the bromine-containing Halons were also destructive to the stratospheric ozone layer, even more so than the CFCs on a molecule-to-molecule comparison basis. Once this connection was made, i t was only a matter of time before Halons became a target for regulatory control. In fact, Halons as a class became the f i r s t group of compounds

This chapter not subject to U.S. copyright Published 1995 American Chemical Society Miziolek and Tsang; Halon Replacements ACS Symposium Series; American Chemical Society: Washington, DC, 1997.

2

HALON REPLACEMENTS


whose p r o d u c t i o n has a l r e a d y been h a l t e d (1 January 1994). T h i s a c c e l e r a t e d c o n t r o l on an otherwise very s u c c e s s f u l f a m i l y of f i r e e x t i n g u i s h i n g agents has l e d t o a high degree of urgency i n terms of i d e n t i f y i n g acceptable replacement f i r e f i g h t i n g agents. T h i s urgency i s being f e l t most a c u t e l y w i t h i n the m i l i t a r y which a b s o l u t e l y needs the h i g h performance f i r e f i g h t i n g a t t r i b u t e s t h a t the Halons have afforded. The search f o r s u c c e s s f u l replacement compounds, u n f o r t u n a t e l y , has proven t o be most d i f f i c u l t , with no "son of Halon" i n s i g h t . The range of requirements t h a t a successf u l replacement compound(s) has t o meet i s q u i t e e x t e n s i v e ranging from acceptable environmental p r o p e r t i e s (Ozone D e p l e t i o n P o t e n t i a l (ODP), G l o b a l Warming P o t e n t i a l (GWP), impact on a i r q u a l i t y and environement), t o c o r r o s i o n e f f e c t s i n long term storage, t o x i c i t y , proper d e l i v e r y characteristics, affordability, and, of course, fire e x t i n g u i s h i n g p o t e n t i a l t o match the p r e s e n t l y used Halons i n volume and weight. At t h i s p o i n t i n time, the r e s e a r c h and t e s t i n g community has evaluated a l l of the obvious and some of the not so obvious replacement compounds and has found t h a t a l l of them are l a c k i n g f o r one reason or another, f o r most a p p l i c a t i o n s ( p a r t i c u l a r l y the m i l i t a r y ones) where high performing agents are r e q u i r e d . As mentioned i n the p r e f a c e , we have reached a type of p l a t e a u i n our search f o r Halon replacements and thus t h i s i s an e x c e l l e n t time t o summarize and r e f l e c t upon the s t a t u s of t h i s search. T h i s book i s d i v i d e d i n t o 5 s e c t i o n s . These are: E n v i r o n ment and P o l i c y ; Technology, T e s t i n g , and New Approaches; Flame E x t i n c t i o n Phenomenology; Flame Suppression Mechanist i c S t u d i e s ; and Fundamental Supporting Science. The chapters i n the f i r s t s e c t i o n deal p r i m a r i l y with the b a s i s f o r the phase-out of the Halon compounds, r e s u l t s of s t u d i e s on the atmospheric chemistry of p o t e n t i a l replacement compounds, and e f f o r t s t o assess the atmospheric e f f e c t s of replacement compounds on g l o b a l ozone l e v e l s and c l i m a t e . The focus of replacement s t r a t e g i e s has been t o f i n d compounds having very s h o r t t r o p o s p h e r i c l i f e t i m e s with r e s p e c t t o r e a c t i o n with atmospheric OH r a d i c a l s or t o p h o t o l y s i s . Much e f f o r t has gone i n t o determining r e a c t i o n mechanisms and the subsequent f a t e of r e a c t i o n products. The concern here has been t h a t the products of the atmos p h e r i c degradation of replacement compounds must themselves not c o n t r i b u t e t o ozone d e p l e t i o n or c l i m a t e m o d i f i c a t i o n . Homogeneous and heterogeneous processes have t h e r e f o r e been s t u d i e d i n great d e t a i l . T h i s kind of r e s e a r c h has i d e n t i f i e d d i f f e r e n t c l a s s e s of p o s s i b l e replacement compounds, such as the HFCs or HCFCs, having " s a t i s f a c t o r y " r e g u l a t o r y r e l a t e d p r o p e r t i e s (at t h i s time) i n terms of atmospheric l i f e t i m e and the benign nature of the r e a c t i o n products. However, the search f o r Halon replacements has not been

Miziolek and Tsang; Halon Replacements ACS Symposium Series; American Chemical Society: Washington, DC, 1997.

1. MIZIOLEK ET AL.

An Overview

3


r e s t r i c t e d t o r e l a t i v e l y s h o r t - l i v e d compounds such as the HFCs or HCFCs, s i n c e many f u l l y f l u o r i n a t e d compounds such as the p e r f l u o r o c a r b o n s (PFCs) have good f i r e suppressant properties. These compounds have the advantage of not having any e f f e c t on the ozone l e v e l s . However, they have the disadvantage of possessing extremely long l i f e t i m e s , which combined with the f a c t t h a t they are s t r o n g i n f r a r e d absorbers i n the 8-12 micron "window" r e g i o n , means t h a t they w i l l c o n t r i b u t e very s i g n i f i c a n t l y t o g l o b a l warming. Environmental c o n s t r a i n t s as a p p l i e d t o many of the potent i a l Halon replacements d i s c u s s e d i n the chapters mean t h a t other c l a s s e s of compounds and other "non-chemical" approaches, such as the use of water mists or p a r t i c u l a t e s , are under c o n s i d e r a t i o n . The p e r f l u o r o a l k y l i o d i d e s have good p r o p e r t i e s as f i r e suppressants, but t h e i r atmospheric f a t e needs c o n s i d e r a b l e f u r t h e r study t o e s t a b l i s h whether tropospheric degradation leads t o harmless by-product formation. The r o l e of i o d i n e i n c o n t r i b u t i n g t o ozone depletion i s now reasonably w e l l - e s t a b l i s h e d , and i s considered i n one of the chapters i n t h i s s e c t i o n . Since i o d i n e i s more e f f i c i e n t than e i t h e r bromine or c h l o r i n e i n ozone d e p l e t i o n , a c r i t i c a l c o n s i d e r a t i o n i s t h a t the i o d i n e i n a f i r e suppressant not penetrate the s t r a t o s p h e r e . There are other c l a s s e s of compounds which are a l s o p o t e n t i a l Halon replacements, such as unsaturated halogen compounds, the halogenated ethers, phosphorus h a l i d e s , and v a r i o u s m e t a l l i c compounds. In some cases these compounds or t h e i r h y d r o l y s i s products are t o x i c and t h e i r atmospheric f a t e s are o f t e n not known i n d e t a i l . Much more l a b o r a t o r y r e s e a r c h i s t h e r e f o r e r e q u i r e d before these can be s e r i o u s l y considered i n terms of Halon replacements. I t must be recognized t h a t none of the suggested replacement compounds possesses a comparable combination of p r o p e r t i e s r e l a t e d t o f i r e suppression, minimum-toxicity, and ease of h a n d l i n g than does CF Br. F i n d i n g a replacement having these propert i e s as w e l l as the property of being a t m o s p h e r i c a l l y neutral, presents r e s e a r c h e r s with an e x t r a o r d i n a r i l y complex and d i f f i c u l t c h a l l e n g e . 3

S e c t i o n I I addresses a number of the a p p l i c a t i o n s , t e s t i n g , and i n i t i a l c h a r a c t e r i z a t i o n i s s u e s of emerging c l a s s e s of replacement compounds i n c l u d i n g f l u o r i n a t e d i o d i n e s and amines. T h i s s e c t i o n covers the s p e c i f i c Army, Navy, and a i r c r a f t requirements as w e l l as the r e s u l t i n g Halon replacement programs being c a r r i e d out by the m i l i t a r y services. However, the m i l i t a r y i s not the only o r g a n i z a t i o n t h a t r e q u i r e s high performance f i r e extinguishment technology. The Alaskan North Slope gas and o i l p r o d u c t i o n f a c i l i t i e s have a unique requirement of e x p l o s i o n i n e r t i o n . T h i s i n e r t i o n requirement adds y e t another c h a l l e n g e f o r Halon replacement compounds s i n c e the chemical and/or p h y s i c a l a c t i o n s t h a t leads t o e f f i c i e n t f i r e extinguishment


HALON REPLACEMENTS

4 do not n e c e s s a r i l y a l s o r e s u l t with regard t o f i r e avoidance.

i n the optimal

performance

A few of the chapters i n S e c t i o n I I address some of the other c r i t i c a l a t t r i b u t e s necessary t o develop s u c c e s s f u l Halon replacement compounds, namely t o x i c o l o g y and c o r r o s i v ity. The t o x i c o l o g y i s s u e p e r t a i n s t o both the e f f e c t on humans due t o the r e l e a s e of the pure agent, as w e l l as t o the p o s s i b l e p r o d u c t i o n of t o x i c combustion byproducts d u r i n g use i n f i r e extinguishment. As i s p o i n t e d out r e p e a t e d l y throughout the book, present c h e m i c a l l y - a c t i v e candidate replacement agents produce c o n s i d e r a b l y g r e a t e r q u a n t i t i e s of t o x i c compounds such as HF and CF 0 d u r i n g use than do the Halons. Downloaded by 80.82.77.83 on September 19, 2017 | http://pubs.acs.org Publication Date: May 5, 1997 | doi: 10.1021/bk-1995-0611.ch001

2

S e c t i o n I I I c o n t a i n s a number of papers d e s c r i b i n g l a b o r a t o ry experiments with emphasis on the g l o b a l behavior of combustion systems i n the presence of i n h i b i t o r s . The r e s u l t s show t h a t the f l u o r i n a t e d compounds which do not c o n t a i n bromine do not have the f i r e suppressing c a p a b i l i t y of Halon 1301. The r e s u l t s a l s o lead t o a data base of s p e c i f i c compounds upon which t h e o r i e s can be t e s t e d . P a r t i c u l a r l y noteworthy i s the development of a detonat i o n / d e f l a g r a t i o n tube method f o r t e s t i n g the e f f e c t i v e n e s s of flame f i g h t i n g agents through the determination of the extent they d e c e l e r a t e the propagating wave and attenuate the hazardous shock t h a t precedes the combustion process. These data r e p r e s e n t a new c h a l l e n g e f o r those who seek t o g i v e a physico-chemical e x p l a n a t i o n of f i r e suppression. I t i s very encouraging t h a t the d e t o n a t i o n / d e f l a g r a t i o n tube has been shown t o be a good p r e d i c t o r of a i r c r a f t dry bay fires. The paper on HF r e p r e s e n t s a new aspect of the problems a r i s i n g from the replacement of Halon 13 01. The r e s u l t s are a demonstration of the i n c r e a s i n g l a b o r a t o r y c a p a b i l i t y t o probe v a r i o u s aspects of the f i r e s i t u a t i o n . S e c t i o n IV c o n t a i n s experimental r e s u l t s where chemical species i n f o r m a t i o n i n a p p r o p r i a t e combustion systems ( l a r g e l y premixed l a b o r a t o r y burners) are t e s t e d a g a i n s t the r e s u l t s of s i m u l a t i o n s . The experimental methodology i s w e l l e s t a b l i s h e d and understood and the r e s u l t s can be considered a c r u c i a l t e s t of the v a l i d i t y of the simulat i o n s . T h i s i s because f i t s of s p e c i e s i n f o r m a t i o n are most s e n s i t i v e t o e r r o r s i n the hydrocarbon/air/halogen k i n e t i c and thermodynamic data base. Thus, the s u b s t a n t i a l agreements t h a t have been obtained suggest t h a t the e s s e n t i a l f e a t u r e s of chemical flame suppression have indeed been captured i n the s i m u l a t i o n . Therefore, one should have c o n s i d e r a b l e confidence i n u s i n g the data base as a semiquantitative predictive tool. For example, one can now successfully differentiate between contributions from d i l u t i o n , heat c a p a c i t y , and chemistry i n w e l l d e f i n e d systems. Another use of such data i s t o t e s t reduced


1. MIZIOLEK ET AL.

An Overview

5


mechanisms. The task of r e l a t i n g s i m u l a t i o n s of nont u r b u l e n t l a b o r a t o r y flames t o a c t u a l f i r e s i s , perhaps, the most s e r i o u s challenge. The l a s t s e c t i o n (V) deals with the fundamental chemistry of f i r e suppression. Two papers d e s c r i b e t h e e f f o r t s a t NIST focussed on the development of a chemical k i n e t i c and thermodynamic information upon which the s i m u l a t i o n s can be based. These two papers may represent some of t h e most important c o n t r i b u t i o n s i n t h i s volume from a general p o i n t of view. C e r t a i n l y , the s t a r t i n g p o i n t of a l l f u t u r e s i m u l a t i o n s w i l l be based on the data from these e f f o r t s . These papers are notable f o r t h e i r systematic r e l i a n c e on theory f o r f i l l i n g t h e gaps i n the data base. T h i s i s due t o the i n c r e a s i n g r e l i a b i l i t y of t h e o r e t i c a l e f f o r t s and the f a l l - o f f i n experimental e f f o r t s i n chemical kinetics. Thus, i t i s s i g n i f i c a n t t h a t i n t h i s volume there i s only one chapter t h a t contains traditional experimentallygenerated chemical k i n e t i c data. T h i s can be c o n t r a s t e d with the s i t u a t i o n i n the e a r l i e r volume e d i t e d by Gann [1]. T h i s i s unfortunate, s i n c e there i s a constant need t o validate and i n many instances calibrate theoretical p r e d i c t i o n s . T h i s i s p a r t i c u l a r l y the case f o r p r e d i c t i o n s on the s t r u c t u r e s and e n e r g e t i c s of the t r a n s i t i o n s t a t e . I t should be noted t h a t t h i s data base i s not r e s t r i c t e d t o f i r e suppression. I t i s indeed a p p l i c a b l e t o a l l small organic systems where f l u o r i n a t e d compounds p l a y a r o l e , f o r example d e s t r u c t i o n of these f l u o r i n a t e d compounds v i a i n c i n e r a t i o n . I t a l s o forms the f l u o r i n a t e d p o r t i o n of the data base f o r systems where f l u o r i n e i s a component; f o r example i n the i n c i n e r a t i o n of some chemical agents. Furthermore, i t can p l a y an important r o l e i n p r e d i c t i n g the nature of the f l u o r i n a t e d compounds t h a t may be formed during combustion. F i n a l l y , because t h i s data base draws on an a c t i v e research area, i t s p r o v i s i o n a l nature must be recognized. One expects t h a t i n time accuracy l i m i t s w i l l be v a s t l y increased and t h a t p r e d i c t i o n s w i l l be much more r e l i a b l e . There i s thus a need f o r a c o n t i n u i n g program t o upgrade the data base. One notes t h a t the estimated accuracy of the thermodynamics d e r i v e d from theory i s of the order of 8 kJ/mol. For species c o n c e n t r a t i o n a p p l i c a t i o n s t h i s i s e q u i v a l e n t t o an e r r o r of a f a c t o r of 30 a t room temperature; 2.5 a t 1000 K and 1.6 a t 2000 K. C l e a r l y , the s i m u l a t i o n s should reproduce broad trends under combustion c o n d i t i o n s , but cannot be r e l i e d on f o r room temperature applications. I t i s q u i t e evident and understandable t h a t t h e search f o r Halon replacements has concentrated on chemicals t h a t are near cousins such as the hydrofluorocarbons (HFCs) and p e r f l u o r o c a r b o n s (PFCs). However, these " c h e m i c a l - a c t i n g " compounds a r e only one general c l a s s of f i r e e x t i n g u i s h e r s . The other major class, the "physically-acting" agents/techniques, u n f o r t u n a t e l y , are not w e l l - r e p r e s e n t e d


6

HALON REPLACEMENTS


i n t h i s book. These i n c l u d e p a r t i c u l a t e or p y r o t e c h n i c a l l y generated a e r o s o l s [ 3 ] , s o l i d p r o p e l l a n t gas generator agents, water and water-based mists, d e f l a g r a t i o n generated a e r o s o l s , and g e l l e d f i n e p a r t i c l e dry chemicals. The primary reason these are not i n c l u d e d i n t h i s book i s t h a t they a r e r e l a t i v e l y new technologies and techniques and not yet w e l l - s t u d i e d . A l s o , i n some cases there i s t h e i s s u e o f the information being company p r o p r i e t a r y [3]. F i n a l l y , as a minor p o i n t , we would l i k e t o address t h e matter of nomenclature. Over the i n t e r v e n i n g 20 years s i n c e the f i r s t book there has been a d e f i n i t e s h i f t from "halon abcde" (see Preface, r e f . 1) t o "Halon abcde". Perhaps i t i s due t o the developments i n the s t r a t o s p h e r i c ozone d e p l e t i o n f i e l d where the compounds have been r e f e r e d t o as "CFCs" not " c f c s " . In any event, as the reader w i l l see, we have made no e f f o r t t o t r y t o impose a standard n o t a t i o n i n t h i s book. As f a r as the e d i t o r s are concerned, both n o t a t i o n s are acceptable, although the argument t o keep t h e n o t a t i o n as o r i g i n a l l y developed i s r a t h e r compelling. References 1. Gann, R.G., Ed., "Halogenated F i r e Suppressants", ACS Symposium S e r i e s 16, American Chemical S o c i e t y , Washington, D.C., 1975. 2. "America Burning: The Report of the N a t i o n a l Commission on F i r e Prevention and C o n t r o l : U.S. Government P r i n t i n g O f f i c e , Washington, D.C. 20402, 1973. 3. Estee Jacobson, Spectrex Inc., Cedar Grove, NJ, p r i v a t e communication. RECEIVED August 11,1995


Halon Replacements: An Overview - ACS Symposium Series (ACS

Recommend Documents