Astm stp 1284 1996

STP 1284 Fire Resistance of Industrial Fluids George E Totten and Jiirgen Reichel, Editors ASTM Publication Number (PCN) 04-012840-12 ASTM 100 Barr Harbor Drive West Conshohocken, PA 19428-2959 Library o f C o n g r e s s C a t a l o g i n g - I n - P u b l i c a t i o n Data F i r e r e s i s t a n c e of I n d u s t r i a l fluids l George E T o r t e n and J u r g e n Reichel p cm - - (ASTM s p e c l a l t e c h n t o a ] p u b l i c a t i o n ; 1284) "Papers p r e s e n t e d a t t h e Symposium o f t h e same name, h e l d in Ind,anapolis, IN on 20 June 1995 s p o n s o r e d by ASTM Committee 002 on Petroleum P r o d u c t s and L u b r i c a n t s " - - F o r e w o r d Includes btbllographtcal references and ~ndex ISBN - - - (alk p a p e r ) F i r e t e s t i n g - - C o n g r e s s e s H y d r a u l i c f l u i d s - - T e s t i n g -Congresses I T o r t e n , George E I I , R e ~ c h e ] , J u r g e n , 1938III American S o c i e t y f o r T e s t i n g and M a t e r i a l s Committee - on Petroleum P r o d u c t s and L u b r i c a n t s IV S e r i e s TH9446.HgF57 1996 821,2 dc20 96-4044 CIP Copyright 1996 AMERICAN SOCIETY FOR TESTING AND MATERIALS, West Conshohocken, PA All rights reserved This material may not be reproduced or copied, in whole or in part, in any printed, mechanical, electronic, film, or other distribution and storage media, without the written consent of the publisher Photocopy Rights Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by the AMERICAN SOCIETY FOR TESTING AND MATERIALS for users registered with the Copyright Clearance Center (CCC) Transactional Reporting Service, provided that the base fee of $2.50 per copy, plus $0.50 per page is paid directly to CCC, 222 Rosewood Dr., Danvers, MA 01923; Phone: (508) 750-8400; Fax: (508) 750-4744 For those organizations that have been granted a photocopy license by CCC, a separate system of payment has been arranged The fee code for users of the Transactional Reporting Service is 0-8031-2041-9/96 $2.50 + 50 Peer Review Policy Each paper published in this volume was evaluated by three peer reviewers The authors addressed all of the reviewers' comments to the satisfaction of both the technical editor(s) and the ASTM Committee on Publications To make technical information available as quickly as possible, the peer-reviewed papers in this publication were prepared "camera-ready" as submitted by the authors The quality of the papers in this publication reflects not only the obvious efforts of the authors and the technical editor(s), but also the work of these peer reviewers The ASTM Committee on Publications acknowledges with appreciation their dedication and contribution to time and effort on behalf of ASTM Printed in Scranton, PA March 1996 Foreword This publication, Fire Resistance of Industrial Fluids, contains papers presented at the symposium of the same name, held in Indianapolis, IN on 20 June 1995 The symposium was sponsored by ASTM Committee D2 on Petroleum Products and Lubricants George E Totten of Union Carbide Corporation in Tarrytown, NY and Jiirgen Reichel of Deutsche Montan Technologie (DMT) in Essen, Germany presided as symposium chairmen and as the editors of the resulting publication Table of Contents Overview Introduction vii ix The Need for S t a n d a r d i z a t i o n of F i r e Resistance Testing of I n d u s t r i a l F l u i d s - A V B R A N D A O Combustion Fire Chemistry of I n d u s t r i a l F l u i d s - - J s NEWMAN Characteristics of Pool Fire B u r n i n g - - A HAMINS, T KASHIWA~I, AND R R B U C H 15 F i r e Resistance Testing Procedures: A Review and Analysis E TOTrEN AND G M W E B S T E R 42 S t a n d a r d i z a t i o n Activities for Testing of Fire Resistant F l u i d s - - j REICHEL 61 F i r e Resistant H y d r a u l i c Fluids a n d Fire Resistance Test Methods Used by the A i r F o r c e - - c E S N Y D E R , JR A N D L J G S C H W E N D E R 72 F i r e Resistance Tests for Fluids a n d L u b r i c a n t s - - T h e i r Limitations a n d M i s a p p l i c a t i o n - - w D PHILLIPS 78 A Review of Phosphate Ester Fire Resistance Mechanisms a n d Their Relevance to Fluid Testing T A MAROLEWSK~AND E D WEre 102 General View a n d Critical Considerations of S p r a y Ignition Tests in Fire-Resistance Evaluation of H y d r a u l i c F l u i d s - - w HEYN 110 Testing and Evaluation of Fire-Resistant H y d r a u l i c Fluids Using the Stabilized Heat Release S p r a y Test K HOLKE 119 S p r a y F l a m m a b i l i t y of H y d r a u l i c F l u i d s - - M M KHAN 133 Implementation of Revised Evaluations of Less Flammable H y d r a u l i c F l u i d s - - A v 8RANDAO 148 Flammability Screening and F i r e H a z a r d of I n d u s t r i a l F l u i d s Using the Cone C a l o r i m e t e r - - A F G R A N D A N D J O T R E V I N O 157 Ease of Extinction An Alternative Approach to Liquid Flammability-G L NELSON 174 Overview Industrial fires caused by the use of flammable fluids such as mineral oils may lead to devastating loss of human lives and property Therefore, many industrial processes such as underground mining, steel rolling, die casting, aerospace, and others require the use of fluids that provide substantially greater fire resistance than those attainable with mineral oils In fluid power applications, this need has led to the development of various classes of fireresistant hydraulic fluids which include polyol ester, phosphate ester, water-in-oil and oil-inwater emulsions, high-water-based fluids, and water-glycol hydraulic fluids Although these and other types of fire-resistant hydraulic fluids are now available, the degree and mechanism of fire resistance that each provides is not the same From the viewpoint of insurance underwriters, labor organizations, government regulation, and the industry itself, it is becoming increasingly critical to be able to determine appropriately the relative fire resistance provided by the use of a particular fluid in a specific industrial process This typically cannot be done with the use of a single fire resistance test, particularly the various spray flammability tests that have been traditionally used by various organizations in the United States and Europe It has been nearly 30 years since a symposium focusing on fire resistance testing of industrial oils in general, and hydraulic fluids in particular, has been held Since that ASTM symposium, which was held in 1966, there have been considerable developments in testing procedures for modeling fire risks involved with a particular industrial process and for discriminating the fire resistance offered by a particular hydraulic fluid This is reflected by the institution of a new fire resistance testing procedure used by Factory Mutual Research Corporation and by the different fire resistance testing procedures required by the 7th Luxembourg Report This symposium will provide a forum for the discussion of the current and future global status of fire resistance testing of industrial oils, primarily hydraulic fluids and turbine oils Four specific areas will be covered: fundamental principles, historical and current testing methodologies and limitations, spray flammability tests, and new test methods Two fundamental aspects of fluid flammability will be discussed One is the often ignored issue of the potential toxicity of fluid combustion byproducts that may be formed The second aspect of fire resistance testing that will be discussed in detail is modeling and characteristics of pool fire burning which is important when the fire risk potential of fluid leaks and spills must be considered To provide a thorough treatment of fire resistance testing, an overview and analysis of the various hydraulic fluid testing procedures, including traditional and current testing procedures, have been reported The objective of these reviews is to identify the limitations and deficiencies of these various tests All of these tests model only one type of fire risk, for example, spray ignition or pool fire burning Thus, it is usually necessary to use two or more tests to provide an adequate assessment of the fire risk that may be encountered However, many of these tests, although they have been used for many years, not adequately reflect the fire risk involved with the use of a particular fluid The inability of these tests to discriminate adequately fire risk will be discussed in the various papers presented here Fortunately, very significant advances have been made in the testing of the fire risk potential of hydraulic fluids Two tests that are currently being promoted for this purpose are the Factory Mutual Research Corporation "Spray Ignition Parameter" test, which will bevii viii OVERVIEW come one of the primary fire resistance testing procedures in the United States, and the "Relative Ignitability (RI)-Index" derived from the newly developed Buxton Test, which will become one of the primary testing procedures required in Europe The testing procedures for both tests and the results obtained for various types of aqueous and nonaqueous hydraulic fluids wilt be discussed Most of the tests require large volumes of fluid and often can only be conducted by relatively few laboratories (often at high cost) With few exceptions, the reproducibility of these tests is relatively poor and many not adequately model the actual relative fire risk encountered Therefore, the identification of much smaller scale, lower cost methods for characterizing fire resistance offered by a particular hydraulic fluid is of great interest The potential use of two calorimetric testing procedures for the evaluation of hydraulic fluid fire resistance will be discussed here From these papers, it is clear that significant gains have been made in modeling and quantifying the relative amount of fire resistance exhibited by a hydraulic fluid Incorporation of the more recently developed testing procedures into harmonized national and international standards will become increasingly important with globalization of safety standards One of the most significant results of this conference may be the possibility for harmonizing global fire resistance testing standards George E Totten Jiirgen Reichel Union Carbide Corporation Tarrytown NY; symposium chairman and editor Deutsche Montan Technologie (DMT) Essen, Germany; symposium chairman and editor Introduction Common industrial fluids include: mineral oils, synthetic hydrocarbon blends, and chemical compositions formulated with additives to achieve properties required for specific applications Potential fire resistance and environmental and toxicological properties of these fluids are composition dependent In hydraulic fluid power systems, power is transmitted and controlled through a liquid under pressure within a closed circuit Petroleum oils are the most commonly used hydraulic fluid Petroleum oils are also commonly used for turbine governor controls and other hydraulic systems in electrical power stations Some applications demand a greater degree of fire resistance than afforded by petroleum oils In these situations, fire-resistant fluids may be used Fire resistance is defined by the ability of the fluid to ignite and propagate flame Fire resistance properties vary widely among the types of fluids Examples of fluids commonly used for their fire-resistant properties include: phosphate esters, polyol esters, thickened water/glycols, and high water base and invert emulsions However, fire-resistant fluids are not completely inflammable They may present some degree of fire risk The hazard will be especially serious if those fluids are used either in close or explosion-prone environments such as those present in underground mining applications or in highly safety sensitive areas such as the aerospace industry Fire-resistant fluids are also commonly used in the steel, aluminum, and die casting industries Therefore, the use of industrial fluids, such as hydraulic fluids, in fire- or explosion-prone areas are subject to regulations regarding the amount of fire resistance that they must provide The benefits of fluid power over electromechanical drives include: smaller size, higher energy efficiency, and ease of adjustment All of these advantages are lost if an incident occurs in which the hydraulic fluid, under pressure, is sprayed in the presence of an ignition source resulting in a fire Three factors required for a fire are: an inflammable fluid, a source of ignition, and oxygen If one of these components is lacking, combustion will not occur Sprays from a hydraulic system may be caused by hose breaks, pinholes, cracks in fittings or measuring connections that failed to resist the load of pulsation, defective sealing elements, and mechanical damage by external influences Sprays of easily inflammable petroleum oil will ignite in the presence of an ignition source whether the system has an operational pressure of 40 or 400 bar Even the removal of the source of ignition will not help flame extinction Fire-resistant fluids, however; may exhibit either fire-inhibiting or even self-extinguishing properties This symposium will address the vital question of proper assessment of fire resistance of industrial fluids Basic principles in fire resistance characterization will be discussed This will be followed by a discussion of standardization activities and current and recent test methodology development There will be a comprehensive discussion on spray ignition tests and novel test methods and an assessment of these methods will be provided X OVERVIEW In specification development, it must be assured that potential hazards will not give rise to exaggerated safety requirements that will lead to technically unreliable applications This would be intolerable not only for economic reasons but would also restrict many applications of fluid power technology Operational safety and economics are imperative in fluid power technology! Hydraulic fluids represent only one element of the system and cannot be replaced indiscriminantly with no risk We are very fortunate that the experience gathered in the United States and Europe during the past 35 years in the development of fire-resistant hydraulic fluids and test methods to determine fire resistance can be presented here in one forum Hopefully, as a result of this meeting, both national and international standards test methods for the determination of fire resistance for individual applications in the different industrial applications can be harmonized in the future NELSON ON EASE OF EXTINCTION 175 The f l a m m a b i l i t y of any m a t e r i a l is not a single property, but r a t h e r a c o m b i n a t i o n or series of properties: ignition, flame spread, heat release, ease of extinction, smoke, toxicity These d e p e n d both on the m a t e r i a l and on e n v i r o n m e n t s or conditions P r a c t i c a l fluid f l a m m a b i l i t y is p e r h a p s more c o m p l e x than that of a solid in that the v o l a t i l i t y of the f l u i d plays a key role in its f l a m m a b i l i t y performance I n d e e d flash point is v e r y m u c h r e l a t e d to volatility (5) Figure shows a plot of flash point versus b o i l i n g point for a large n u m b e r of compounds Part of the s c a t t e r is due to the fact that data f r o m several flash point apparatus were used C o n c e n t r a t i o n s of a fuel in the v a p o r space above a l i q u i d will d e p e n d on the free space above the fuel and thus affect the result For m i x t u r e s the relative amounts of c o n s t i t u e n t s will also be affected (6) Flash point data are by far the m o s t f r e q u e n t l y r e p o r t e d data for the f l a m m a b i l i t y of fluids Both flash point and fire point have a s s o c i a t e d issues (7) Heat r e l e a s e rate t e s t i n g of fluids has i n v o l v e d b o t h l a b o r a t o r y and larger scale assessment (8) In m o r e recent a p p r o a c h e s results have been r e p o r t e d on the use of the cone c a l o r i m e t e r to assess l i q u i d flammability The cone heater has b e e n u s e d to assess the i g n i t a b i l i t y of h e x a d e c a n e and crude oils (9) Full rate of heat release data have b e e n r e p o r t e d for silicones (I0) and for pesticides Heat release data for h y d r o c a r b o n s are of the order of 1600 k W / m at 60 k W / m e x t e r n a l flux, s i m i l a r to low heat, n o n - f l a m e retardant polymers Silicones above a d e g r e e of p o l y m e r i z a t i o n of 15 are o n e - t e n t h that figure Short chain s i l i c o n e s h o w e v e r had RHR of over 2000 k W / m 2" Other e f f o r t s with heat release rate c a l o r i m e t r y are r e p o r t e d in this volume One test w h i c h has also been u s e d by 50-100 l a b o r a t o r i e s for fluids is that of o x y g e n index O x y g e n index, of course, has b e e n u s e d e x t e n s i v e l y for s o l i d p o l y m e r samples (ASTM D2863) : m o l d e d polymers, fabrics, c e l l u l a r plastics, and thin films For a review see (Ii) OXYGEN INDEX Oxygen index is a m e a s u r e of ease of extinction W h i l e a c h a r a c t e r i s t i c of a material, it is a f l a m m a b i l i t y limit and as such is d e p e n d e n t upon o x i d i z e r flow (oxidants other than o x y g e n may be used), fuel geometry, a n d test c o n f i g u r a t i o n as well as t e m p e r a t u r e and pressure The oxygen index is the p e r c e n t a g e of oxygen in an o x y g e n / n i t r o g e n a t m o s p h e r e which will just s u s t a i n c o m b u s t i o n of a material The concept of o x y g e n index derives from work on gases and liquids For example, Simmons and W o l f h a r d s t u d i e d the b u r n i n g of fuels at the surface of a p o r o u s h e m i s p h e r i c a l burner, fuels r a n g i n g from hydrogen, carbon monoxide, low m o l e c u l a r w e i g h t hydrocarbons, alcohols, and benzene (12) D a t a have also b e e n r e p o r t e d for l i q u i d s using a glass wick t e c h n i q u e (to study o r g a n o p h o s p h o r u s liquids) (13) By far the largest amount of data on liquids has been r e p o r t e d u t i l i z i n g a small ceramic r e s e r v o i r c o n t a i n i n g liquids or fusible solids r e p l a c i n g the usual p o l y m e r sample in a s t a n d a r d oxygen index test apparatus (14-15) See Figure Copyright by ASTM Int'l (all rights reserved); Sat Dec 26 18:59:00 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 176 FIRERESISTANCEOF INDUSTRIALFLUIDS 400 PLOTOF FLASHPOINT ~o,V~Up~,, / 300 I-0Q = 200 (/) _J LI- :, I00 , Wf'- , ]" 100 200 , I , I i I 300 400 500 BOILINGPOINT~ , I 600 , I I 700 FIG - - P l o t of f l a s h p o i n t v e r s u s b o i l i n g p o i n t f o r a l a r g e n u ~ e r of compounds D a t a f r o m s e v e r a l f l a s h p o i n t a p p a r a t u s a r e used ~ F [ ] I ~I ~ il J~ ~ Pilotflame specimen N~O2supply FIG - - O x y g e n i n d e x t e s t a p p a r a t u s m o d i f i e d for u s e w i t h l i q u i d s a n d p o w d e r s N / O s u p p l y p r o v i d e s N / O m i x t u r e s of p r e c i s e c o n c e n t r a t i o n s a n d is d i s c u s s e d in A S T M D T h e o x y g e n i n d e x is t h e m i n i m u m p e r c e n t of o x y g e n i n t h e o x y g e n n i t r o g e n ~ x t u r e which will just sustain co~ustion NELSON ON EASE OF EXTINCTION 177 The t e c h n i q u e is: a sample is p l a c e d in a c e r a m i c r e s e r v o i r in the test chamber Prior to ignition, the % oxygen f l o w i n g t h r o u g h the OI c y l i n d e r is a d j u s t e d to a level higher than that e x p e c t e d for c o m b u s t i o n of the test sample A f t e r ignition w i t h a h y d r o g e n or p r o p a n e flame, the sample is a l l o w e d to b u r n for 10-20 seconds to a c h i e v e a steady state With the flame b u r n i n g in a smooth m o t i o n l e s s state the % 02 is s l o w l y r e d u c e d until the flame begins to wave or oscillate The onset of u n s t e a d i n e s s is a useful signal and u s u a l l y occurs w i t h i n one oxygen index unit of the e n d point The end point is the final % 02 which just b a r e l y supports combustion This p e r c e n t a g e is the o x y g e n index It is p r e c i s e and reproducible Sample size and g e o m e t r y of the r e s e r v o i r were found to have little p r a c t i c a l effect for most materials The t e c h n i q u e has been a p p l i e d to some 1000 simple o r g a n i c compounds Data for some 600 liquids and fuseable solids are l i s t e d in the A p p e n d i x to this paper A plot of oxygen index versus n u m b e r of c o m p o u n d s at each value is given in F i g u r e M i x t u r e s give v a r i a b l e results d e p e n d i n g upon the total time to d e t e r m i n a t i o n of end point This is to be e x p e c t e d as the gaseous fuel c o m p o s i t i o n will v a r y as the more v o l a t i l e c o m p o n e n t is d e p l e t e d f r o m the reservoir E x p e r i m e n t s such as a d d i t i o n of Sb203 to b r o m o c y c l o h e x a n e show no change in oxygen index Temperatures reached in the cup are no h i g h e r than the b o i l i n g point of the m a t e r i a l b e i n g tested For m a t e r i a l s which char or ash on burning, some w o r k e r s have shown a s u b s t a n t i v e d e p e n d e n c e of oxygen index on r e s e r v o i r (cup) diameter, with larger cups g i v i n g lower oxygen indicies Plots of e x t i n c t i o n time versus % 02 in the a t m o s p h e r e allow e x t r a p o l a t i o n of the oxygen index (16) Similar b e h a v i o r has been o b s e r v e d in heat r e l e a s e tests (17) V o l a t i l i t y has l i m i t e d impact on oxygen index values Simple h y d r o c a r b o n s are in a range of 15-17 w h e t h e r pentane, p e t r o l e u m h y d r a u l i c fluid, jet fuel, m i n e r a l oil, or p o l y p r o p y l e n e U s i n g this t e c h n i q u e one can learn m u c h of the c h e m i s t r y of flame r e t a r d a n c y of organic s t r u c t u r e s (11,18) A n d o x y g e n index can be u s e d to e v a l u a t e m a t e r i a l s in a v a r i e t y of e n v i r o n m e n t s (19,20) A very d e t a i l e d t h e o r e t i c a l treatment of oxygen index has b e e n p e r f o r m e d by A Murty Kanury (21) Oxygen index is d e p e n d e n t upon the e x p e c t e d p h y s i c o c h e m i c a l p r o p e r t i e s of the system, that is of a small pool fire Others have d e v e l o p e d e m p i r i c a l r e l a t i o n s h i p s to e s t i m a t e oxygen indicies for liquids (22) OXYGEN INDEX VERSUS SPRAY FLAMMABILITY It is i n t e r e s t i n g that the earliest u t i l i z a t i o n of the concept of o x y g e n index is a study of the f l a m m a b i l i t y of oil mists, w h i c h was r e p o r t e d by Sullivan, Wolfe, and Zisman in 1947 (23) The p a r a m e t e r m e a s u r e d was c a l l e d the ~spray f l a m m a b i l i t y limit." The test m e a s u r e d the m i n i m u m p e r c e n t a g e of oxygen r e q u i r e d to allow p r o p a g a t i o n of a flame in an oil mist in a c l o s e d c h a m b e r after ignition by an e l e c t r i c a l arc The f l a m m a b i l i t y of l u b r i c a t i n g and h y d r a u l i c oils for aircraft were of p a r t i c u l a r interest in their study Table (14,15,23) gives s e l e c t e d results for the l i m i t i n g oxygen c o n c e n t r a t i o n s as m e a s u r e d by their 178 FIRE RESISTANCE OF INDUSTRIAL FLUIDS 80 6O z 20 , m m 15 20 25 30 35 40 Oxygen Index 45 m am-m 50 FIG Plot of oxygen index versus n u m b e r of c o m p o u n d s for 600 fluids and powders listed in appendix TABLE I Compound i I0 ii 12 13 14 15 16 17 18 19 20 Oxyqen Indicies a n d Spray F l a m m a b i l i t y ~or S e l e c t e d Compounds Spray F l a m m a b i l i ~ y Diethyl ether Benzene Cumene n-Hexadecane B-Methoxymethoxyethanol Trioctylphosphate Aniline Chlorobenzene Tricresyl p h o s p h a t e ~-Chloronaphthalene Tributyl p h o s p h a t e o-Diehlorobenzene Dichlorodiphenylether Ethylene glycol Diethylene glycol 1,2,4-Trichlorobenzene A r o c l o r 1242 Trimethyl p h o s p h a t e A r o c l o r 1248 Hexaehlorobutadiene ii 12 12 12 12 13 14 14 19 27 27 29 33 40 42 44 45 47 64 77 LimiD 55 m 60 at each value Limit~ Oxyg@n Index 16.5 15.9 15.2 15.5 13 18 16 19 22 19 20 23 21 14 13 30 33 23 365 54 NELSON ON EASE OF EXTINCTION 179 t e c h n i q u e c o m p a r e d w i t h oxygen indicies as m e a s u r e d for the same m a t e r i a l s by N e l s o n and W e b b (14,15) Figure shows a plot of oxygen index v e r s u s the spray f l a m m a b i l i t y limit for each m a t e r i a l listed W h i l e there is some curvature, there is c o n s i d e r a b l e c o r r e l a t i o n b e t w e e n the two techniques C o m p o u n d s 14 and 15, the g l y c o l s seem to be out of place, however, since they burn readily E s t i m a t e d errors in the Naval R e s e a r c h L a b o r a t o r y work were r e p o r t e d to be • 1% in the lower ranges a n d • 2% in the h i g h e r ranges C o m p a r i s o n of t h e i r results w i t h i n c e n d i a r y fire e x p e r i m e n t s (bullets) s h o w e d that fluids h a v i n g a v a l u e of over 45-50 in the spray test s h o w e d no i n c i d e n c e of fire in the i n c e n d i a r y tests As can be seen in F i g u r e 4, this c o r r e s p o n d s to an o x y g e n index of 29-32, similar to the v a l u e s of about 27 taken for m a r g i n a l fire r e t a r d a n c e in the case of polymers SUMMARY In summary, m e a s u r e m e n t of the oxygen index of l i q u i d s p r o v i d e s a d i f f e r e n t v i e w of l i q u i d flammability Unlike the f l a s h - p o i n t test, the oxygen index is not a direct function of v o l a t i l i t y nor is it a m e a s u r e of ease of ignition; but rather an e x t i n c t i o n - r e l a t e d phenomenon The o x y g e n index of liquids has been u s e d to e v a l u a t e a n d compare a n u m b e r of i n d u s t r i a l l y i m p o r t a n t fluids such as h y d r a u l i c fluids, l u b r i c a t i n g oils, s i l i c o n e fluids, and others W i t h oxygen i n d e x of liquids as a tool, the e l u c i d a t i o n of chemical s t r u c t u r e - f l a m m a b i l i t y relationships, is m a d e easy Given the ease with w h i c h the o x y g e n index of liquids can be measured, its use and c o m p a r i s o n w i t h other t e c h n i q u e s is to be encouraged 70 e20 ~_ - =_ m -J ; ~ 50 ~ 40