1

FLAME INHIBITION BY PHOSPHORUS-CONTAINING COMPOUNDS 

FINAL TECHNICAL REPORT 

March 1998 

E. M. Fisher, F. C. Gouldin, T. M. Jayaweera, M. A. MacDonald 

Sibley School of Mechanical and Aerospace Engineering 

Upson Hall, Cornell University, Ithaca, NY 14853-7501 

DARPA Contract MDA972-97-M-0013 

Sponsored by: 

The Department of Defense 

Strategic Environmental Research and Development Program 

The views and conclusions contained in this document are those of the authors and should not be 

interpreted as representing the official policies, either expressed or implied, of the Strategic Environmental 

Research and Development Program, the Defense Advance Research Projects Administration (DARPA), 

or any other part of the U.S. Government. 
2

TABLE OF CONTENTS

I. Summary 

 A. Task Objectives 1 

 B. Technical Problems 1 

 C. General Methodology 1 

 D. Technical Results 2 

 E. Important Findings and Conclusions 3 

 F. Significant Hardware Developments 4 

 G. Special Comments 4 

 H. Implications for Future Research 4 

II. Papers and Articles Presented and Submitted for Publication 5 

A. Presentations 5 

 B. Submitted for Publication 6 

III. Detailed Project Description 6 

 A. Experimental Apparatus and Techniques 7 

 1 Burner and Related Equipment 7 

 2 Determination of Strain Rates 8 

 3. Technique for Approaching Extinction 9 

 4. Operating Conditions and Chemicals 17 

 B. Extinction Results 19 

 1. Undoped Pure Fuel vs. Pure Air Flames and Premixed Flames 19 

 2. Nitrogen in Pure Fuel vs. Pure Air Flames 20 

 3. DMMP and TMP in Pure Fuel vs. Pure Air Flames 21 

 4. Isooctane in Pure Fuel vs. Pure Air Flames 23 

 5. Argon in Methane/Nitrogen vs. Oxygen/Nitrogen Flames 24 

 6. DMMP in Methane/Nitrogen vs. Oxygen/Nitrogen Flames 26 

 7. DMMP in Premixed Methane/Air Flames 30 

 C. Literature Search 31 

 D. Important Findings and Conclusions 32 

IV. Unresolved Technical Problems 35 

V. Recommendations for Additional Research 36 

VI. Conclusions 37 
3

VII. References 38 

APPENDIX A. Literature Search Results 40 
4

I. SUMMARY

I A. Task Objectives

The objective of this project is to evaluate the effectiveness of phosphorus-containing compounds 

(PCCs) as alternatives to halons as fire suppressants. PCCs show promise as flame inhibitors but have 

been little studied in the past. Our objective is to assess the effectiveness of several PCCs as flame 

suppressants under a variety of flame conditions, using by determining their effect on extinction strain rate 

in an opposed-jet burner. These measurements provide a basis for deciding whether this class of 

compounds merits further study as halon alternatives. Another objective is to obtain information about 

whether the chemical form of the phosphorus plays an important role in flame inhibition. 

I B. Technical Problems

The main technical problem in evaluating PCC flame suppression effectiveness 

was developing a reliable method for performing extinction measurements with lowvapor-pressure additives. A novel method of approaching extinction was developed and 

validated. This method allows the use of syringe-pump delivery of low-vapor-pressure 

additives, while avoiding the problem of transient additive loading as flowrates are 

varied. 

I C. General Methodology

The experimental methodology used in this study was the measurement of extinction strain rates 

in laminar opposed-jet-burner flames. Phosphorus-containing compounds (PCCs) were added to flames, 

and their effect on the extinction strain rate was determined. The fractional reduction in extinction strain 

rate was taken as a measure of suppression effectiveness. 

Extinction measurements were performed with two PCCs, dimethyl methylphosphonate (DMMP, 

P(=O)(-CH3)(-OCH3)2) and trimethyl phosphate (TMP, P(=O)(-OCH3)3), as minor flame additives. Several 

types of flames were investigated with DMMP: pure methane vs. pure air, pure propane vs. pure air, 

premixed methane/air, and various choices of methane/nitrogen vs. oxygen/nitrogen. With TMP, only pure 

methane vs. pure air flames were investigated. Several experiments were performed with inert additives, 

for comparison. Fuel-side and air-side introduction of the additive were investigated in separate 

experiments. Maximum additive levels were limited to about 1500 ppm to avoid additive condensation. 

In addition to experiments, a literature search on the physical, toxicological and materials 

compatibility properties of phosphorus-containing compounds was performed. We compiled data about as 

many PCCs as possible from several reference works. 
5

I D. Technical Results

The PCC additives demonstrated high flame suppression effectiveness under all conditions investigated. 

When introduced on the air side of pure methane vs. pure air flames, the PCCs showed an effectiveness 

that was two to four times higher (on a molar basis) than values reported in the literature for CF3Br, a 

highly effective halon flame suppressant for which replacements are sought. PCC effectiveness is 40 

times higher (on a molar basis) than that of N2, determined through our own measurements. Effectiveness 

was linear with loading, and was not strongly influenced by the choice of fuel or by whether the flame was 

premixed or nonpremixed. The flame suppression properties of PCCs are very unlikely to be due to their 

hydrocarbon groups, as experiments with isooctane addition to the air side of a methane/air flame produced 

flame promotion rather than suppression. Under no circumstances was flame promotion by PCCs 

observed. 

Experiments with variable-dilution methane/nitrogen vs. oxygen/nitrogen flames showed, as 

expected, that the flame location has a strong impact on additive effectiveness. Fuel-side addition became 

more effective as the stoichiometric mixture fraction increased, and air-side effectiveness showed the 

opposite trend. When results were normalized by the quantity of additive calculated to be at the flame 

location, two additional observations were made. (1) Air-side delivery of DMMP to the flame produces 

significantly higher effectiveness per mole additive at the flame location than fuel-side delivery does. (2) 

The effectiveness of DMMP has a strong temperature dependence, with lower effectiveness at higher 

adiabatic flame temperatures. This implies that DMMP flame suppression performance in practical fires, 

which typically have lower temperatures than those of this study[1], may be even better than that observed 

here. 

A literature search for physical, toxicological, and materials compatibility properties of PCCs was 

performed, collecting data on 57 compounds. This or similar information can be used to optimize the 

choice of candidate halon replacements. Most of the compounds listed have low vapor pressure, implying 

that delivery to the flame in sufficient quantities may require application of the agent in droplet form, either 

as a pure substance or dissolved in water. PCCs span a wide range of toxicity. Materials compatibility data 

are sparse, and are not available for several promising compounds. The available information indicates 

several PCCs are compatible with some metals (stainless steel, Hastelloy, Inconel) and incompatible with 

others (copper, aluminum, brass). Compatibility with non-metals is fairly good with the exception of 

Buna-N. More research appears to be needed in this area. 

I E. Important Findings and Conclusions

In the current series of experiments, the PCCs TMP and DMMP have shown high 

flame suppression effectiveness for a variety of nonpremixed flames and for a more 

limited set of premixed flames. Over the range of conditions tested, effectiveness is 
6

linear in loading, and increases as temperature decreases. The extinction results also lead 

to several tentative conclusions about the mechanism by which PCCs suppress flames. 

Although the current experiments provide no direct information about the mechanism of 

action, the high effectiveness of PCCs suggests a chemical mechanism, as opposed to a 

physical one. Since PCCs’ molar effectiveness is even higher than that of CF3Br, a 

plausible mechanism might involve catalytic radical recombination pathways in which 

active suppressant species are recycled. The higher effectiveness (when normalized by 

the quantity of additive at the flame) of air-side vs. fuel-side delivery of the PCCs also 

supports this idea, as it suggests that the loading of additive in the region of high radical 

levels is important. The very similar effectiveness for DMMP and TMP and the flame 

promotion observed with hydrocarbon additives, are consistent with the hypothesis that 

phosphorus-containing species formed in the flame, rather than the parent phosphoruscontaining compound or its hydrocarbon groups, are key participants in flame 

suppression reactions. 

I F. Significant Hardware Developments

The use of the present burner in extinction measurements with low-vapor-pressure additives is 

new to this study. This use has required the development of a novel method of approaching extinction. In 

this method, the flowrate of the doped reactant stream is kept constant, while that of the other stream is 

increased. As a result, the flame position changes during the approach to extinction. To validate this 

method, we empirically determined that the extinction strain rate is affected only slightly by flame position 

over a wide range of positions. Extinction measurements in this acceptable region of the burner were 

considered valid. 

I G. Special Comments

None. 

I H. Implications for Further Research

The extremely favorable flame suppression properties of PCCs revealed by this study indicate that 

this class of compounds merits further research as potential halon replacements. Several types of research 

would be useful. 

First, research is needed on methods of delivering large quantities of relatively low-vapor-pressure 

PCCs to the flames. For practical applications, it will be necessary to achieve loadings higher than the 
7

1500 ppm achieved here, and considerably higher than the few hundred ppm achievable without preheating 

of reactants. Options for flame delivery include sprays of solid particulates or droplets of either neat PCCs 

or PCC/water solutions. 

Secondly, it would be useful to test the flame suppression effectiveness of a broader range of 

PCCs. The current experiment involves two fairly similar PCC molecules. Extending this type of study to 

other compounds will either strengthen or disprove the hypothesis that the phosphorus content of a 

molecule is its most important attribute. In the coming year, we plan to build a delivery system for fine 

droplets that will eventually allow us to test a much broader range of candidate PCCs in our burner. 

Thirdly, research into the mechanism of flame suppression by PCCs would be of use in optimizing 

the choice of PCC for halon replacement. Experiments involving measurements of important chemical 

species, especially flame radicals and active species containing phosphorus, would be of great use in 

narrowing the range of possible mechanisms responsible for flame suppression. In the coming year we 

will be developing capabilities for making measurements of the OH radical, one of the key species believed 

to be affected by the presence of phosphorus. 

Finally, it is necessary to investigate materials compatibility, toxicity, and likely global 

environmental impact of candidate halon replacements. Of these areas, materials compatibility appears to 

be the one in which the need for more information is most pressing. 

II. PAPERS AND ARTICLES PRESENTED AND SUBMITTED FOR 

PUBLICATION

II A. Presentations

T. M. Jayaweera, M. A. MacDonald, E. M. Fisher, F. C. Gouldin, “A novel method for evaluationg the 

effectiveness of low volatility flame inhibitors with an opposed-jet burner,” presented at the Fall Technical 

Meeting of the Eastern States Section, The 

Combustion Institute, Hartford, CT, October 1997. 

M. A. MacDonald, T. M. Jayaweera, E. M. Fisher, F. C. Gouldin, “Inhibition of non-premixed flames with 

dimethyl methylphosphonate,” presented at the Spring Technical Meeting of the Central States Section, 

The Combustion Institute, Point Clear, AL, April, 1997. 

 

M. A. MacDonald, T. M. Jayaweera, E. M. Fisher, F. C. Gouldin, “Inhibited counterflow nonpremixed 

flames with variable stoichiometric mixture fraction,” presented at the Fall Technical Meeting of the 

Eastern States Section, The Combustion Institute, Hartford, CT, October 1997. 

II B. Submitted Publications
8

M. A. MacDonald, T. M. Jayaweera, E. M. Fisher, F. C. Gouldin, “Variation of chemically active and inert 

flame suppression effectiveness with stoichiometric mixture fraction,” submitted to the 27th Symposium 

(International) on Combustion, The Combustion Institute, December 1997. 

M. A. MacDonald, T. M. Jayaweera, E. M. Fisher, F. C. Gouldin, “Inhibition of non-premixed flames by 

phosphorus-containing compounds,” submitted to Combustion and Flame, August, 1997. 

III. DETAILED PROJECT DESCRIPTION

III A. Experimental Apparatus and Techniques

Experiments were conducted in an opposed-jet burner equipped for use with lowvapor-pressure additives. This burner, which was built for a previous research project, is 

shown in Fig. 1. The following sections describe the burner, the methods of determining 

the strain rate, the method of approaching extinction, and the experimental conditions and 

chemicals used in the experiments. 

Exhaust

Heater

DMMP

Injection

Measured

Oxidizer

Flow

Measured

Fuel Flow Heater

Heated

N2 Sheath

Heated

N2 Sheath

N2

Purge

Video

Camera

s flame

Fuel N2

Air N2

Pyrex

Enclosure

Figure 1. Schematic of the Opposed-Jet burner 

III A 1. Burner and Related Equipment

The burner was constructed from straight, open glass tubes 30 cm long with an ID 

of 0.98 cm, and a separation distance of 0.95 cm between opposing nozzles. No screens 
9

or obstructions are used. Annular sheath flows of nitrogen are provided through 2.22-cm 

ID glass tubes. The sheath tube exits are offset by approximately 1 cm, upstream of the 

reactant tube exits, to minimize the impact of the sheath flow on the development of the 

reactant flows. The burner was aligned vertically with the lower tube used as the fuel 

source and the upper tube as the oxidizer source. Results of a few experiments conducted 

with the reverse orientation to study the effect of buoyancy showed no significant change 

in extinction strain rate. A flat flame is produced when the oxidant and fuel stream 

velocities are such that the flame is situated in the central portion of the space between 

the burner nozzles. When the flame is close to either nozzle, it exhibits curvature toward 

the nozzle. The entire burner is isolated in a glass enclosure for control of exhaust gases. 

This enclosure is purged with nitrogen and maintained slightly below atmospheric 

pressure. The enclosure has a glass window on one end, approximately 25cm from the 

centerline of the flow. A video camera, located a few centimeters from this window, was 

used to measure flame position. Measurements of flame position were made from 

magnified images from the camera, displayed on a television screen. Flame position was 

measured relative to the oxidizer nozzle exit plane using the separation gap between the 

nozzles for reference. 

The PCC additives are liquids at room temperature with low vapor pressures (less 

than one torr at ambient temperature). In order to maintain sufficient concentrations of 

the PCC additives in the vapor phase, the reactant lines were heated to approximately 

100°C with electrical heating tapes. Wall temperatures on the outside surface of the 

heated lines were measured with adhesive thermocouples. The temperature of the 

reactant streams 10 cm upstream from the exit of the nozzles was maintained at 100±1°C 

via active control of the sheath flow temperature. These final reactant temperatures were 

measured by sheathed thermocouples in direct contact with the gas flow. The liquid PCC 

additives was added to the reactant streams via a syringe pump that provides a constant 

volume flow. The gas flow at the injection site was preheated to approximately 130 °C 

for a rapid vaporization of the liquid PCC additive. The liquid density, syringe size, and 

motor speed fixed the mass flow rate of the additive during a given experiment. Previous 

pyrolysis experiments with DMMP and TMP [2, 3] have shown that thermal 

decomposition is negligible below 1000 K; thus the preheating of the reactant streams 

should have no effect on their chemical composition. Mass-flow controllers, supplied by 
10

MKS Industries, were used to measure reactant flow rates for the gas-phase reactants: 

methane, propane, nitrogen, oxygen, and various mixtures of these compounds. 

III A 2. Determination of Strain Rates

Strain rates at extinction were determined from fuel and oxidant flowrates, using the following 

expression: 

Strain rates determined in this way are referred to as global strain rates. 

In Eqn. 1, VF and VO respectively represent the average velocities of the fuel and oxidant streams leaving 

the burner nozzles, as determined from the measured mass flow rates at extinction. ρF and ρO, the densities 

of the fuel stream and oxidant, are evaluated at 100 °C. These strain rates will be referred to as global 

extinction strain rates. The strain rate expression was derived by Seshadri and Williams [4] for the case of 

plug flow at the nozzles with an infinitesimally thin reaction zone. Under those conditions, the expression 

represents the strain rate at the oxidant side of the reaction zone. Although the conditions of our 

experiments clearly differ from those assumed by Seshadri and Williams, recent work at the Naval 

Research Laboratory[5] has found a proportional relationship between global strain rates, determined from 

Eqn. 1, and maximum local velocity gradients upstream of the flame, measured by laser-doppler 

velocimetry. A proportionality is likely to hold for our burner as well, because of the very similar 

dimensions and geometry of the burners used in the two studies. 

We present extinction data in several forms. For undoped flames, we report the extinction strain 

rate, aqo, as calculated in Eqn. (1). The subscript o refers to the undoped condition. For flames with an 

additive, we present the extinction strain rate normalized by the corresponding undoped value (aq /aqo) or 

the reduction in strain rate at extinction normalized by the corresponding undoped value ((aqo - aq)/aqo). 

The latter quantity will be called the effectiveness. In some doped cases, the quantity of additive at the 

flame location is estimated through a numerical calculation. In these cases, we also report an effectiveness 

per mole additive calculated to be at the flame, sometimes called the normalized effectiveness. 

III A 3. Technique for approaching extinction.

In determining extinction conditions for use in calculating aq, we made use of a 

novel method of approaching extinction, motivated by a need to minimize transient 

effects of additive loading. Commonly, extinction studies with opposed-jet burners 

adjust the strain rate by varying both the oxidizer and fuel streams simultaneously. With 

our choice of a constant-mass-flowrate syringe pump for delivering the additive to one of 

the reactant streams, the conventional procedure results in a change in additive loading 

during the extinction process. With low-vapor-pressure additives like the PCCs studied 

1 (1) 2

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = +

O O

O F F

q

V

V

L

V

a

ρ

ρ
11

here, this changing concentration may produce transients in adsorption or desorption on 

the tubing and burner walls, and lead to uncertainty in the true loading of additive in the 

flows at the exit plane of the doped reactant stream at extinction. 

The novel method presented here is an alternative technique to circumvent the 

difficulties associated with additive loading transients. During our experiments, the 

concentration of additive in the relevant reactant stream (fuel or oxidizer) was fixed by 

maintaining constant flowrates of all the constituents of the doped reactant stream. After 

waiting a sufficient time for equilibrium conditions to be established, we approached 

extinction by varying only the flowrate of the undoped stream. One consequence of 

using this method is that the positions of both stagnation plane and flame move towards 

the doped-stream nozzle during the extinction experiment. This was found to have only a 

minor influence on the measured extinction strain rate except when the flame or 

stagnation plane was very close to one of the nozzles, as described below. 

We took an empirical approach to validating our novel method of approaching 

extinction. Experiments were performed over a large range of flow rates of the methane 

and air streams, achieving extinction with the flame in a variety of positions. Figure 2 

shows the resulting global extinction strain rates (aq) as a function of the measured flame 

position. In this figure, flame positions inside either nozzle are plotted at the appropriate 

nozzle location (0 or 9.5 mm from oxidizer nozzle). Extinction strain rate varies 

systematically with flame position, but the variation is small over a large central portion 

of the region between the burner nozzles. The global extinction strain rate varies less 

than (±2% from a mean value of 359 s-1 for flame positions between 0 and 7mm. This 

region of consistent global extinction strain rates will be referred to as the acceptable 

region. For experiments in which extinction occurs with the flame outside the acceptable 

region, large deviations in aq occur. Also shown in Fig. 2 are sets of data from two series 

of experiments conducted with a 300 ppm doping of DMMP and 50,000 ppm doping of 

N2, both in the oxidizer stream. The limited number of data points in the DMMP series is 

a result of the coarsely quantized mass flow rates of dopant available from the syringe 

pump. Because of the inhibitory effect of the DMMP or N2 additive, these data sets have 

markedly lower mean global extinction strain rates than the data for undoped methane 

vs. air flames. However, both data sets show the same systematic trends with flame 

position, and both have only small variations in extinction strain rate over the central 

acceptable region between 0 and 7 mm. 
12

240

260

280

300

320

340

360

380

0 2 4 6 8 10

50000 ppm N2

Undoped

300 ppm DMMP

Global Extinction Strain Rate [s-1]

Observed Flame Location

[mm from oxidizer nozzle]

Figure 2. Variation of global extinction strain rate, aqo, s-1, with observed flame position 

at extinction. Methane vs air flames: undoped, doped with DMMP, and doped with N2. 

Zst=0.054 

A similar acceptable region was found with propane-air non-premixed flames, 

and is presented in Figure 5 below. In comparison to the methane experiments, these 

propane flames exhibited considerably more flutter and larger scatter in the observed 

global extinction strain. However, in the acceptable region, the observed global 

extinction strain was still found to be within 2.5% of the mean value of 489 s-1. 

The existence of the same acceptable region for a range of flame extinction strain 

rates establishes the validity of our method for approaching extinction. Provided that the 

flame position at extinction lies within this region, the results should be consistent to 
13

within ±2% (methane/air) or 2.5% (propane/air) of those obtained using more 

conventional methods that maintain a nearly constant flame position. Caution should be 

exercised in using this method to measure small changes in strain rate because of the 

small but systematic variation of flame extinction strain rate with flame position. 

The asymmetrical dependence of extinction strain rate on flame position appears to be 

due to the offsetting of the flame to the oxidant side of the stagnation plane, which is 

conveniently characterized using the stoichiometric mixture fraction, Zst. (See Section III 

A 4 for a definition and discussion of Zst.) The importance of this displacement was 

investigated by performing a series of measurements in which flame and stagnation plane 

were coincident. Results from these conditions, for methane/nitrogen vs. oxygen/nitrogen 

flames with Zst = 0.50 with YO = 0.387 and YF = 0.097, are shown in Fig. 3. During these 

experiments, in which the oxidizer stream was mixed from separate oxygen and nitrogen 

source bottles, the global extinction strain rate was very sensitive to the concentration of 

oxygen. This sensitivity contributed to the greater scatter in the Zst = 0.50 tests than in 

the pure fuel vs. pure air tests, which were conducted with a premixed oxidizer source. 

Nonetheless, the global extinction strain rate varies less than ±3% of the mean value of 

336 s-1 for flame locations between 0 and 9mm. Within experimental scatter, results with 

Zst = 0.5 are symmetrical about the center of the region between the two burners. 
14

280

300

320

340

360

380

0 2 4 6 8 10

Global Extinction Strain Rate [s-1]

Observed Flame Location 

[mm from oxidizer nozzle]

Figure 3. Variation of global extinction strain rate, aqo, s-1, with observed flame position 

at extinction. Methane/nitrogen vs oxygen/nitrogen flames. Zst=0.5 

Although the acceptable region of Figures 2 and 3 is defined in terms of the 

observed flame position, in practice it is not necessary to determine the experimental 

observation of flame location at extinction for all measurements. Rather, a parameter S is 

introduced which can be calculated from the reactant stream properties at the nozzles. 
15

S approximates the distance from the oxidizer nozzle to the stagnation plane and is given 

by the expression in Eqn. 2, again derived by Seshadri and Williams for plug flow 

boundary conditions [4]: 

Figure 4 shows a plot of observed flame location for both Zst = 0.50 and Zst = 

0.054 against the parameter S. Methane or a methane/nitrogen mixture is the fuel. It is 

interesting to note that the observed flame location does not vary linearly with the 

predicted location of the stagnation plane, but instead follows a sigmoidal curve, being 

much more sensitive to flow variations when it is near the middle of the separation gap. 

The data presented in Fig.4 shows flame positions for only high strain cases (275-360 s-1). 

It was found that, in general, the steepness of the sigmoidal curve increased with 

increasing strain rates. For purposes of conducting experiments with the new method, it 

suffices to observe that the flame location, for each condition, is a well-correlated one-toone function of this parameter S. Therefore, one can map the experimentally determined 

acceptable region in terms of S, and direct observation of flame position becomes 

unnecessary. For both pure methane vs. pure air (Zst = 0.054) this region is 3.5 mm < S < 

5.25 mm. For methane/nitrogen vs. oxygen/nitrogen with Zst =0.5, the region is 3.5 mm 

< S < 6.0 mm. For pure propane vs. pure air (Zst =0.059), the region is 3.5 mm < S < 5.25 

mm. The extinction strain rate data for the propane vs. air flames are shown as a function 

of S in Fig. 5 below. All extinction results reported below were for flames inside the 

more conservative acceptable region obtained for the pure fuel vs. pure air flames. 

1 (2) ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = +

O O

F F

V

V

S L

ρ

ρ
16

0

2

4

6

8

3456

Z = 0.054

Z = 0.50

Observed Flame Position 

[mm from oxidizer nozzle]

S [mm from oxidizer nozzle]

st

st

Figure 4. Observed flame positions as a function of predicted distance to the stagnation 

plane (Eq. 2). Results are shown for nonpremixed methane vs. air flames (Zst =0.054) 

and methane/nitrogen vs. oxygen/nitrogen flames (Zst =0.5). 
17

460

480

500

520

540

3 3.5 4 4.5 5 5.5 6

Global Extinction Strain Rate [s-1]

S [mm from oxidizer nozzle]

Figure 5. Variation of global extinction strain rate, aqo, s-1, with observed flame position at 

extinction. Undoped propane vs air flames. Zst=0.059 
18

III A 4. Operating Conditions and Chemicals

We performed several series of extinction experiments. The stoichiometric mixture 

fraction, Zst, provides a convenient way of characterizing the nonpremixed flames. Zst is 

the fraction of the material present at the stoichiometric contour that originated in the fuel 

stream. Zst can be evaluated from reactant compositions in the nozzles and the 

stoichiometry of the overall combustion reaction, using Eqn. 3 

where Y is mass fraction, MW is molecular weight, ν is the stoichiometric coefficient for 

complete combustion, the subscripts O and F refer to oxygen and fuel respectively, and 

the subscripts ±∞ refer to conditions at the fuel and oxidizer nozzles. With the 

assumption of equal diffusivities for all species, setting Zst = 0.50 places the flame at the 

stagnation plane. Larger and smaller values of Zst correspond respectively to flames on 

the fuel and oxidant side of the stagnation plane. 

Initially, we performed experiments with pure methane vs. pure air and with pure 

propane vs pure air; these flames, respectively, have Zst = 0.054 and 0.059, and 

correspond to a flame position well on the oxidant side of the stagnation plane. Other 

experiments were performed with methane/nitrogen vs. oxygen/nitrogen mixtures. In 

these experiments, Zst was varied systematically. Since the value of Zst depends on two 

independent variables, YF and YO, fixing Zst leaves one degree of freedom on reactant 

concentrations. Except where noted, unique conditions were established by choosing the 

mass fraction of oxygen to give the same undoped global extinction strain rate as was 

obtained for the pure methane vs. pure air flame. As Zst is increased with fixed aqo, Tad

declines steadily, as seen in Fig. 6. 

(3)

, ,

,

∞ ∞

∞

+ ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ =

F O

F F

O O

o

st

Y Y

MW

MW

Y

Z

ν

ν
19

2050

2100

2150

2200

2250

2300

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

Adiabatic Flame Temperature (K)

Zst

Figure 6.Adiabatic flame temperature as a function of stoichiometric mixture fraction for 

methane/nitrogen vs. oxygen/nitrogen flames with aqo held constant at 350±10 s-1. Error 

bars represent standard deviation of data. 

A limited number of experiments were performed with twin premixed flames. In 

these experiments, identical stoichiometric methane/air mixtures flowed from each 

nozzle. 

The PCC additives used during this investigation, dimethyl methylphosphonate 

(DMMP, P(=O)(-CH3)(-OCH3)2) and trimethyl phosphate (TMP, P(=O)(-OCH3)3), were 

supplied by Aldrich Chemical Company and used without further purification (stated 

purity of each compound: 97%). The chemically inert additives nitrogen (99,998% pure) 

and argon (99.999% pure) supplied by MG Industries. Several series of pure fuel vs. 

pure air extinction measurements were conducted using premixed oxygen and nitrogen 

(21±0.2% oxygen mole fraction) or Ultra Zero Grade air (21±2% oxygen mole fraction, 

total hydrocarbon content <0.1 ppm) as the oxidizer and methane (99% pure) or propane 

(99.5% pure) as the fuel. All gases were supplied by MG industries. For other extinction 

experiments, involving premixed flames and variable Zst, oxygen (99.994% pure) was 

mixed with nitrogen (99.998% pure) in measured proportions to form the oxidizer 

stream, and the fuel was diluted with nitrogen (99.998% pure). 
20

III B. Extinction Results

III B 1. Undoped Pure Fuel vs. Pure Air Flames and Premixed Flames

Initial tests were conducted with undoped reactant streams at ambient temperature 

to compare results from our experimental apparatus with those of other researchers. For 

undiluted methane burning in air, our measured undoped global extinction strain rate was 

aqo =296 s-1. Variation in aqo up to 80 s-1 has been observed with different bottles of high 

purity compressed air, and is attributed to slightly different batch mass fractions of 

oxygen. However, extinction measurements on undoped flames using the same oxidizer 

source are consistent to within ±5 s-1. All results for doped flames presented herein are 

normalized to undoped experiments under identical conditions, i.e. using the same 

oxidizer source. This value is comparable to the value found by Puri and Seshadri [6] of 

280 s-1 and to the value of 255 s-1, computed from flow rates at extinction reported by 

Papas et al. [7]. All three numbers fall within the range of variation attributed to 

differences in composition of high purity air batches. This agreement is surprisingly 

good in light of the significantly different boundary conditions and aspect ratio of the 

burner used by Puri and Seshadri. Our measured global extinction strain rate differs 

significantly from literature values of local extinction strain rate, which range from 340 

to 400 s-1 for experiments[7-9] and from 354 to 544 s-1 for numerical calculations [8]. 

Comparable differences between global and local strain rates are observed by other 

researchers[7]. 

For undoped propane vs. air flames, we measured a global extinction strain rate of 

489 s-1 with reactants at 100 °C; we did not perform propane extinction measurements 

with ambient-temperature reactants. Puri and Seshadri [6] report an undoped global 

extinction strain of 305 s-1 with reactant streams at ambient temperature. For methane-air 

flames, we found that preheating reactants to 100 °C increased the global extinction 

strain by 22%. It is expected to have a similar impact on the propane-air flames making a 

direct comparison of our data with the literature difficult. 

For premixed stoichiometric methane/air flames, with reactant streams at 100 °C, 

the measured global extinction strain was 873 s-1. 

III B 2. Nitrogen in Pure Fuel vs. Pure Air Flames
21

Further validation experiments were conducted with nitrogen as a chemically 

inert flame-inhibiting additive. Normalized extinction strain rates for nitrogen addition to 

the air side of a methane/air flame are shown in Fig. 7. 

0.7

0.8

0.9

1

0 15000 30000 45000 60000

Heated N

2

Unheated N

2

N

2

 (literature)

Normalized Global Extinction Strain Rate

Dopant Loading [ppm]

Figure 7. Global extinction strain rate normalized by undoped value (aq/aqo) for N2 as an 

oxidizer-side additive in methane vs. air flames with and without reactant preheating to 

100 °C. Also shown: literature data of Puri and Seshadri [6]. 

Each data point represents the average of at least three measurements, and is normalized 

by the extinction strain rate for a pure methane/air flame. Extinction strain rate drops 

linearly with increasing loading of this additive. Although preheating reactants to 100 °C 

has a significant effect on the undoped strain rate (increasing it from 296 to 360 s-1), Fig. 

7 shows that it has no effect on the normalized results. The nitrogen dilution data can be 

compared to room-temperature data of Puri and Seshadri [6], also shown in Fig. 7. 
22

Agreement is good, with least-mean-square slopes agreeing within 7%. However, it 

should be noted that the diluted flame experiments of Puri and Seshadri were conducted 

at a fixed value of Zst =0.0544. This requires some nitrogen addition to the fuel-side flow 

in contrast to our experiments in which nitrogen was added only to the oxidizer stream. 

Correcting for the effect of this fuel-side addition would lower our measured extinction 

strain rates by about 3%, resulting in an overall discrepancy of 10% with the Puri and 

Seshadri data. 

III B 3. DMMP and TMP in Pure Fuel vs. Pure Air Flames

Figure 8 shows our results for PCC addition to the air stream of pure methane vs. 

pure air flames, with reactants preheated to 100 °C. Each data point represents the 

average of at least three measurements, and strain rates with additive, aq, are normalized 

by the corresponding undoped extinction strain rate, aqo. For DMMP addition, the global 

extinction strain rate is observed to decrease linearly with additive mole fraction. 

Experiments indicate that at a mole fraction of 1500 ppm, aq is reduced by 35% of the 

undoped value. TMP doping of methane-air flames has a very similar effect on 

extinction conditions over the common range of loadings. Detectable inhibition (~3% 

reduction in aq) is found at loadings as low as 100ppm. For mole fractions below 

100ppm, preheating of reactants was not necessary to prevent condensation of DMMP. 

This allowed for ambient-temperature testing of low DMMP loadings which 

demonstrated inhibition effectiveness similar to that found in the preheated experiments. 
23

0.65

0.7

0.75

0.8

0.85

0.9

0.95

1

0 500 1000 1500 2000

TMP

DMMP

Normalized Global Extinction Strain Rate

Dopant Loading [ppm]

Figure 8. Global extinction strain rate normalized by undoped value ( aq/aqo) for DMMP 

and TMP as oxidizer-side additives in methane vs. air flames. 

Figure 9 shows the normalized global extinction strain rate for DMMP addition to 

pure propane vs. pure air flames, with data averaging the same as for the methane/air 

flames above. The greater experimental scatter in these experiments may be associated 

with the visible fluttering of the higher-strain propane air flames. In an effort to reduce 

this flutter by lowering the Reynolds number of the reactant flows an additional series of 

tests was conducted using nozzles with a reduced I.D. of 0.80 cm. The results from these 

experiments are also shown in Fig. 9. The observed normalized extinction strain rate for 

DMMP with the smaller nozzles was found to be in reasonable agreement with our 

standard burner results. Aside from the scatter, both sets of results are very similar to 

those in pure methane vs. pure air flames. 
24

0.75

0.8

0.85

0.9

0.95

1

0 500 1000 1500 2000

Standard Burner

Reduced Diameter

Normalized Global Extinction Strain Rate

Dopant Loading [ppm]

Figure 9. Global extinction strain rate normalized by undoped value ( aq/aqo) for DMMP 

as an oxidizer-side additive in propane vs. air flames. 

III B 4. Isooctane in Pure Fuel vs. Pure Air Flame

We performed an experiment to determine whether the hydrocarbon content of 

the PCCs contributes significantly to the inhibition effectiveness, perhaps by acting as a 

radical sink. Tests were conducted with isooctane as the dopant on the air side of a pure 

methane vs. pure air flame. Isooctane has a similar structure to the PCCs but lacks the 

central phosphorus atom. It is expected that any contribution from methyl groups to 

flame inhibition by the PCCs would be observed during the isooctane tests. However, 

these tests showed a 4% increase in the global extinction strain at a loading of 400 ppm, 

indicating that the effect of the hydrocarbon was to promote the flame, not to inhibit it. 

This result provides support for the hypothesis that the phosphorus atom is crucial to the 

flame inhibition effects of the PCCs studied here. 

III B 5. Argon in Methane/Nitrogen vs. Oxygen/Nitrogen Flames
25

Results from the first series of tests in which Zst varied from 0.2 to 0.7, are shown 

in Fig. 10. Argon is introduced as an oxidizer-side or fuel-side additive, in a series of 

flames. In this case we plot the effectiveness, i.e. the reduction in global extinction strain 

rate normalized by the undoped value, ((aqo - aq)/aqo). Each data point represents the 

average of four extinction measurements. The error bars on the figures represent the 

standard deviation of the observed values, which in this case is larger than the systematic 

error due to the method of approaching extinction. As expected, effectiveness with 

oxidant-side doping decreases as the flame moves towards the fuel side (increasing Zst). 

The converse is true with fuel-side doping. Argon has a diffusivity similar to that of the 

reactants; thus, the quantity present at the stoichiometric contour, which determines its 

effectiveness, should vary roughly linearly with Zst. 

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

oxidant-side doping

fuel-side doping

Effectiveness

Zst

Figure 10. Flame suppression effectiveness of 25,000 ppm argon as an oxidant-side or 

fuel-side additive in methane/nitrogen vs. oxygen/nitrogen flames with fixed aqo. 

Effectiveness is defined as ((aqo - aq)/aqo). Error bars represent standard deviation of data. 

For a quantitative prediction of the amount of additive reaching the flame, we 

performed detailed numerical calculations of the flame structure, using existing Sandia 

codes [10-13] with plug flow velocity boundary conditions and multicomponent diffusion 

but no thermal diffusion. In these calculations, the flame structure was calculated with 

detailed chemistry, using the GRI mechanism [14] with nitrogen chemistry omitted. The 
26

mole fraction of dopant is evaluated at the maximum temperature contour, taken to 

represent the flame location. 

0

1

2

3

4

5

6

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

oxidant-side doping

fuel-side doping

Effectiveness per Mole Ar at Flame

Zst

Figure 11. Normalized flame suppression effectiveness for argon in methane/nitrogen vs. 

oxygen/nitrogen flames with fixed aqo. Effectiveness is normalized by the quantity of 

argon at the maximum temperature location in the flame, as predicted by a numerical 

simulation. Error bars represent standard deviation of data and uncertainty in calculated 

loading. 

Figure 11 depicts the argon results, normalized by the numerically predicted 

quantity of argon present at the maximum temperature contour. These curves of 

effectiveness per mole at the flame show no trend with Zst, indicating that the 

concomitant changes in Tad and flame structure, collectively, have no significant 

influence on the argon effectiveness. Other tests, described below, further demonstrate 

that the argon effectiveness per mole at the flame is independent of Tad. In addition, Fig. 

11 shows no significant difference between oxidizer-side and fuel-side addition for argon 

flame suppression effectiveness per mole at the flame. 

To further clarify the influence of temperature on this system, a series of tests 

were performed for a fixed Zst = 0.055. This experiment was conducted with a fixed 

composition cylinder of oxygen/nitrogen (21%/79% by volume) and fixed additive flow, 
27

greatly reducing experimental uncertainties. Tad was manipulated by varying the reactant 

stream temperatures from 22-112 (±1)°C. This resulted in a range of Tad from 2237-2283 

K. There was a significant influence on the overall flame strength, as seen in the 

variation of aqo from 261-393 s-1. However, the effectiveness for argon at different 

temperatures varied less than 3% and showed no trend with Tad. These results confirmed 

that argon's effectiveness has no temperature dependence. 

III B 6. DMMP in Methane/Nitrogen vs. Oxygen/Nitrogen Flames

Figure 12 shows the results from extinction measurements performed with 

DMMP for Zst between 0.055 and 0.7. The observed effectiveness variation with Zst is 

somewhat more complicated than for the argon tests, although it still follows the same 

general trend. Each data point in Fig. 12 represents the average of 8 extinction 

measurements, with error bars representing the standard deviation of the measured 

values. Differences between individual data points at a given Zst show that tests repeated 

at identical conditions yielded slightly different results. This variation is attributed 

largely to the repeatability of the dopant injection system. The dopant effectiveness may 

also be influenced by small changes in flame temperature resulting from lack of 

repeatability of the reactant stream compositions. The resulting overall experimental 

scatter which we observed was significantly higher than the inert tests. The systematic 

uncertainty due to the method of approaching extinction becomes significant for the 

oxidizer-side addition tests due to the high observed effectiveness. We estimate an 

overprediction between 3 and 15% of DMMP effectiveness for this range of conditions 

due to this systematic uncertainty. The effect is small for the fuel-side addition data. 
28

0

0.05

0.1

0.15

0.2

0.25

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

oxidant-side doping

fuel-side doping

Effectiveness

Zst

Figure 12. Flame suppression effectiveness of 500 ppm DMMP as an oxidant-side or 

fuel-side additive in methane/nitrogen vs. oxygen/nitrogen flames with fixed aqo. 

Effectiveness is defined as ((aqo - aq)/aqo). Error bars represent standard deviation of data. 

The normalized effectiveness results for DMMP, seen in Fig. 13, have some 

interesting features. Firstly, it is notable that the DMMP effectiveness per unit mole 

fraction is roughly 100 times that of argon, indicating strong chemical suppression by 

DMMP. 

Secondly, the curves for oxidizer- and fuel-side addition are offset significantly 

with respect to one another. The oxidizer-side curve in Fig. 13 displays an effectiveness 

roughly twice that of the fuel-side curve. The slight systematic overprediction of the 

oxidizer-side addition effectiveness, described above, would reduce the magnitude of this 

disparity, but would not reconcile the difference in these curves. The difference between 

the curves may reflect the importance of the region of high radical levels in the 
29

0

200

400

600

800

1000

1200

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

oxidant-side doping

fuel-side doping

Effectiveness per Mole DMMP at Flame

Zst

Figure 13. Normalized flame suppression effectiveness for DMMP in methane/nitrogen 

vs. oxygen/nitrogen flames with fixed aqo. Effectiveness is normalized by the quantity of 

DMMP at the maximum temperature location in the flame, as predicted by a numerical 

simulation treating DMMP as inert. Error bars represent standard deviation of data and 

uncertainty in calculated loading. 

suppression process. In most of the flames tested here, key flame radicals are calculated 

to peak on the oxidant side of the flame. Quantities of additive at the peak radical 

locations thus would be lower than at the flame location for fuel-side doping, and higher 

than at the flame location for oxidant-side doping. To test this idea, we performed an 

alternative normalization of the effectiveness, using the quantity of additive calculated to 

be at the location at which the reaction H+O2 → OH +O has its maximum value. This 

location is representative of the region of high radical levels. This alternative 

normalization brings the two curves in Fig. 13 closer together. However, even 

considering systematic error, oxidant-side doping remains more effective. The disparity 

between oxidizer- and fuel-side addition may also be associated with the types and 

quantities of radicals and products that are formed from the parent molecule as it 

approaches the flame from different directions and their relevance to the suppression 

action. If we assume that the important suppression action takes place on the oxidizer 
30

side of the flame, then additives to the fuel stream must travel through the flame to reach 

this point. This may have a significant effect on what phosphorus-containing species are 

present in the region of important radical chemistry for different modes of addition, i.e. 

oxidizer- or fuel-side doping. 

A final feature of Fig. 13 is that for both the oxidizer- and fuel-side tests, the 

normalized effectiveness increases with Zst. The existence of this slope implies that the 

suppressant effectiveness varies with either temperature or structure of the flame, or both. 

Studies in a variety of premixed flames have indicated that at high temperatures (above 

2350 K) [15, 16], DMMP can become a flame promoter. Thus the inhibition 

effectiveness per mole of DMMP at the flame is expected decrease with increasing flame 

temperature. Figure 13 is consistent with this expectation, showing decreasing inhibitor 

effectiveness with increasing adiabatic flame temperature (lower Zst values). However, it 

is possible that changes in flame structure, which occur at different Zst values, may be 

influencing suppressant effectiveness as well. 

Further tests were conducted to clarify this temperature dependence. Due to 

condensation of the dopant below 80°C, we were unable to use control of the reactant 

temperatures to vary Tad over a significant range. Instead, the overall dilution of the 

flame, at a fixed value of Zst = 0.5, was used to vary Tad. In this experiment, the mass 

fraction of oxygen in the oxidizer stream ranged from 0.39 to 0.44, resulting in a Tad

ranging from 2132 to 2261 K and an aqo range of 294 - 572 s-1. Unfortunately, the 

variation in reactant stream compositions increased the susceptibility of the results to the 

sensitivity to random uncertainties in relative flowrates, producing considerable scatter. 

The results from this experiment are shown in Fig. 14, along with the data for oxidizerside addition at fixed aqo, but varying Zst values; all plotted against Tad. Although the 

large experimental scatter makes it difficult to draw quantitative conclusions, a clear 

trend of decreasing effectiveness with increasing Tad is observed, comparable to that seen 

in the constant aqo data. However, these results do not conclusively eliminate the 

possibility of flame structure and the detailed chemistry of dopant action influencing 

dopant effectiveness. 
31

200

400

600

800

1000

1200

2050 2100 2150 2200 2250 2300

fixed undoped extinction strain

fixed Zst

Effectiveness per Mole DMMP at Flame

Adiabatic Flame Temperature (K)

Figure 14. Normalized flame suppression effectiveness for DMMP in methane/nitrogen 

vs. oxygen/nitrogen flames as a function of adiabatic flame temperature. Triangles 

represent varying Zst from 0.1-0.7, fixed aqo=350±10 s-1, while diamonds represent fixed 

Zst=0.5, varying aqo from 294-572 s-1. Effectiveness and error bars as in Fig. 13. 

III B 7. DMMP in Premixed Methane/Air Flames

Limited experiments were performed with DMMP addition to one reactant stream 

in dual premixed stoichiometric methane/air flames. Normalized global extinction strain 

rate results are shown in Fig. 15. Trends are comparable to those in nonpremixed 

methane/air flames. 

Uncertainties in loading are considerably greater for these experiments than for 

the nonpremixed ones because of our method of approaching extinction. We chose to 

dope only one of the premixed reactant streams with DMMP, in order to be able to 

approach extinction by varying the flowrate of an undoped reactant stream. As in the 

nonpremixed flames, diffusion across the stagnation plane produces lower loadings at the 

flame than that in the doped reactant stream. However, in contrast to the nonpremixed 

flames, the flame position relative to the stagnation plane is strongly affected by the 

inhibitory properties of the additive. Thus it is impossible to estimate the true loading at 

the flame without knowledge of the combustion chemistry effects of the PCCs. The 
32

reported loadings can be considered upper bounds on the PCC loading at the flame 

location for the premixed flames. 

0.8

0.85

0.9

0.95

1

Normalized Global Extinction Strain Rate

0 200 400 600 800 1000

Dopant Loading [ppm]

Figure 15. Global extinction strain rate normalized by undoped value ( aq/aqo) for DMMP 

as an additive in one reactant stream of dual premixed stoichiometric methane/air flames. 

III C. Literature Search

A literature search was performed to gather information on relevant properties of PCCs. The 

results of this survey are given in Appendix A, which lists 57 compounds along with available physical 

properties, toxicological information, handling requirements, recommended maximum exposure levels, and 

materials compatibility. If we are correct in believing that the chemical form of the parent compound is not 

crucial to fire suppression, this or similar information can be used to optimize the choice of candidate halon 

replacements. Compounds in Appendix A were selected primarily on the basis of availability of 

information. Several compounds with severe toxicity were deemed unsuitable for fire suppression 

purposes and deliberately excluded from the list. An effort was made to include all available information 

on compounds that have been used in fire-fighting applications or in previous investigations of fire 

suppression. Data in this table is taken largely from hazardous industrial materials handbooks, 

manufacturers’ listings, and publications of the World Health Organization. 
33

Most of the compounds listed have low vapor pressure, implying that delivery to the flame in 

sufficient quantities may require application of the agent in droplet form, either as a pure substance or 

dissolved in water. It is difficult to make generalizations about the toxicity of PCCs. PCCs range in 

toxicity from non-toxic, essential food constituents and FDA approved additives to some of the most toxic 

compounds known (chemical warfare agents) [17]. Halogenated PCCs tend to be among the more toxic. 

As a result of the current study, it is clear that halogen atoms are not a requirement for high flame 

suppression effectiveness. Only limited materials compatibility information was found. This information 

indicates several PCCs are compatible with some metals (stainless steel, Hastelloy, Inconel) and 

incompatible with others (copper, aluminum, brass). Compatibility with non-metals was fairly good with 

the exception of Buna-N. Information was typically unavailable for compounds that were otherwise 

among the most promising as flame suppressants. It is likely that a more detailed literature review, or an 

experimental investigation, will be required in order to obtain needed materials compatibility data. 

III D. Important Findings and Conclusions

Extinction results for PCC additives are summarized in Fig. 16. These results 

show very similar flame suppression effectiveness for DMMP and TMP in suppressing 

methane/air and propane/air nonpremixed flames, and methane/air premixed flames. The 

similar effectiveness of DMMP and TMP is consistent with the hypothesis that it is 

phosphorus radicals formed in the flame that are important and not the parent compound. 

However, it is not a very rigorous test of the hypothesis because DMMP and TMP 

resemble each other fairly closely. 
34

0.5

0.6

0.7

0.8

0.9

1

0 500 1000 1500 2000

Premixed Methane/Air with DMMP 

Non-Premixed Methane vs. Air with TMP 

Non-Premixed Methane vs. Air with DMMP 

Non-Premixed Propane vs. Air with DMMP - Standard Burner

Normalized Global Extinction Strain Rate

Non-Premixed Propane vs. Air with DMMP - Reduced Diameter

Dopant Loading [ppm]

Figure 16. Summary of flame suppression data with PCC additives. 

In Fig. 17 we compare flame suppression effectiveness data for DMMP and TMP 

with literature data [7, 18, 19] for CF3Br, an effective halon fire suppressant for which 

replacements are sought. All data sets are for methane vs. air nonpremixed flames, but 

some of the literature experiments were performed with a Tsuji burner. The flame 

inhibition properties of DMMP are two to four times better, on a molar or mass basis, 

than those reported in the literature for CF3Br. Similar comparisons of DMMP with 

Fe(CO)5, one of the most effective flame suppressants known, show that Fe(CO) 5 is a 
35

0.6

0.7

0.8

0.9

1

0 500 1000 1500 2000

TMP

DMMP

CF

3

Br (Milne et al.)

CF

3

Br (Trees et al)

CF

3

Br (Papas et al.)

Normalized Global Extinction Strain Rate

Dopant Loading [ppm]

Figure 17. Comparison of DMMP and TMP flame suppression data from the present 

study with CF3Br literature data [7, 18, 19]. Methane vs. air flames with air-side 

addition. 

stronger suppressant at low loadings: inhibition at 200 ppm [20] is comparable to the 

PCC's effectiveness at 1500ppm. However, Fe(CO)5's effect as an suppressant plateaus 

for mole fractions between 200 and 500 ppm, the highest gas-phase concentration 

achievable with ambient temperature reactants [20]. The PCCs' suppression performance 

can also be compared to the N2 data presented above: DMMP and TMP are 

approximately 40 times more effective than N2 on a molar basis (~10 times as effective 

on a per mass basis). It is important to note that the range of extinction strain rates 

achieved in these PCC experiments represents only the upper portion of the range of local 
36

strain rates encountered in a realistic, turbulent, fire[21]. Extending the experimental 

range to much lower strains would require a different method of introducing the PCC. 

Two important observations were made in the experiments in which the dilution 

of the two reactant streams was varied. (1) DMMP is significantly more effective as a 

suppressant when added to the oxidizer-side, rather than fuel-side, of the flame, even 

when results are normalized by the calculated quantity of additive at the flame location. 

(2) The effectiveness of DMMP has a strong temperature dependence, with lower 

effectiveness at higher adiabatic flame temperatures. The first observation is consistent 

with the hypothesis that the PCC acts on the flame radicals, which generally have their 

highest values on the oxidant side of the flame. The second observation is consistent 

with previous experiments [16] showing a transition from flame inhibition to flame 

promotion at high temperatures. Over the conditions of our experiments, no promotion 

was observed. DMMP’s temperature dependence implies that flame suppression 

performance in practical fires, which typically have lower temperatures than those of this 

study[1], may be even better than that observed here. 

IV. UNRESOLVED TECHNICAL PROBLEMS

Most technical problems related to measuring extinction strain rates in the presence of low-vaporpressure additives were satisfactorily resolved in the current study. Two unresolved issues remain. First, 

our justification of the novel method of approaching extinction was entirely empirical. We did not 

determine the reasons for the existence of a range of flame positions in which dependence of extinction 

strain rate on flame position is weak. We did not devote time to resolving this issue because we considered 

the empirical justification of the novel method adequate. Secondly, our method of approaching extinction 

can not be applied to premixed flames in which both reactant streams are doped. The only alternative that 

appears to be available for these flames is to approach extinction very slowly, to ensure that 

adsorption/desorption transients are negligible. 
37

V. RECOMMENDATIONS FOR ADDITIONAL RESEARCH

The extremely favorable flame suppression properties of PCCs revealed by this study indicate that 

this class of compounds merits further research as potential halon replacements. Several types of research 

would be useful. 

First, research is needed on methods of delivering large quantities of relatively low-vapor-pressure 

PCCs to the flames. For practical applications, it will be necessary to achieve higher loadings than the 

1500 ppm achieved here, and considerably higher loadings than the few hundred ppm achievable without 

preheating of reactants. Options for flame delivery include sprays of solid particulates or droplets of either 

neat PCCs or PCC/water solutions. Alternatively, if an acceptable PCC with higher vapor pressure can be 

found, it may be possible to use current halon delivery systems with fairly minor modifications. 

Secondly, it would be useful to test the flame suppression effectiveness of a broader range of 

PCCs. The current experiment involves two fairly similar molecules. Extending this type of study to other 

compounds will either strengthen or disprove the hypothesis that the phosphorus content of a molecule is 

its most important attribute. In the coming year, we plan to build a delivery system for fine droplets that 

will eventually allow us to test a much broader range of candidate PCCs in our burner. 

Thirdly, research into the mechanism of flame suppression by PCCs would be of use in optimizing 

the choice of PCC for halon replacement. Experiments involving measurements of important chemical 

species, especially flame radicals and active species containing phosphorus, would be of great use in 

narrowing the range of possible mechanisms responsible for flame suppression. In the coming year we 

will be developing capabilities for making measurements of the OH radical, one of the key species believed 

to be affected by the presence of phosphorus. We plan to use the technique of laser-induced fluorescence 

to measure this species. For a definitive test of proposed mechanisms, it would also be worth while to 

develop methods for making quantitative measurements of the important phosphorus-containing radicals in 

the flame (for example, PO, PO2, HOPO, and HOPO2). Further work in developing and refining detailed 

chemical kinetic mechanisms for phosphorus combustion chemistry will also be needed as species 

measurements become available. 

As toxicological and materials compatibility properties will play an important role in determining 

the viability of PCCs as halon replacements, research in these areas would be of use. At this stage, it may 

be more fruitful to test the fire suppression effectiveness of compounds with good toxicological and 

materials properties than to determine the toxicological and materials properties of compounds with good 

fire suppression effectiveness. Recommendations of compounds or classes of compounds likely to have 

good toxicological and/or materials compatibility properties are needed. If literature data beyond that 

covered in our literature search can not be found, a screening study may be in order. Materials 

compatibility data appear to be especially sparse. 

Finally, it is important to consider the potential global environmental impact of PCCs. Although 

stratospheric chemistry and infrared absorption cross sections for PCCs have not been investigated 

thoroughly to our knowledge, it is likely that short atmospheric lifetimes of these compounds will 

guarantee that global environmental impact will be small. Rate constants for several PCCs’ reactions with 

OH have been measured under atmospheric conditions [22-24]. Atmospheric lifetimes estimated from 
38

these rate constants range from 3.1 days for TMP to under 3 hours for phosphorothioates. These low 

values mitigate against any significant effect on the ozone layer or contribution to global warming by 

PCCs. These conclusions are based on experiments with a limited set of PCCs. If more stable PCCs are 

under consideration, this subject must be revisited. 

VI. CONCLUSIONS

This project assessed phosphorus-containing compounds (PCCs) as alternatives to halons as fire 

suppressants. The flame suppression effectiveness of two PCCs, dimethyl methylphosphonate and 

trimethyl phosphate, was evaluated by determining their effect on the global extinction strain rate in 

opposed-jet flames. For the variety of flames tested, these PCCs showed very high flame suppression 

effectiveness. Their effectiveness was superior to that of the halon CF3Br for nonpremixed methane/air 

flames. For the limited range of PCCs tested, the chemical form of the parent compound appeared to have 

little effect on flame suppression properties. PCCs show promise as halon replacements. Further research 

is needed to investigate their mechanisms of action, to determine important toxicological and materials 

compatibility properties, and to devise effective ways to deliver them to fires. 

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14. Bowman, C. T., Hanson, R. K., Davidson, D. F., Gardiner Jr., W. C., Lissianski, V., Smith, G. P., 

Golden, D. M., Frenklach, M., and Goldenberg, M., "GRI-Mech," Ver 2.11, 

http://www.me.berkeley.edu/gri_mech/. 

15. Lask, G. and Wagner, H. G. 8th Symposium (International) on Combustion 432-438 (1960). 

16. Hastie, J. W. and Bonnell, D. W., “Molecular Chemistry of Inhibited Combustion Systems,” 

National Bureau of Standards, Final NBSIR 80-2169 ; PB81-170375, 1980. 

17. Weil, E. D., "Phosphorus-Based Flame Retardants," in Handbook of Organophosphorus 

Chemistry, Engel, R., Ed. Marcel Dekker, Inc., New York, 1992, pp. 683-738. 

18. Milne, T. A., Green, C. L., and Benson, D. K. Combust. Flame 15:255-264 (1970). 

19. Trees, D., Grudno, A., and Seshadri, K. Combust. Sci and Tech. 124:311-330 (1997). 

20. Reinelt, D. and Linteris, G. T. 26th Symposium (International) on Combustion 1421-1428 (1997). 

21. Grosshandler, W. L., Gann, R. G., and Pitts, W. M., “Evaluation of Alternative In-Flight Fire 

Suppressants for Full-Scale Testing in Simulated Aircraft Engine Nacelles and Dry Bays,” 

National Institute of Standards and Technology NIST SP 861, 1994. 

22. Atkinson, R., Aschmann, S. M., Goodman, M. A., and Winer, A. M. Int. J. Chem. Kinet. 20:273-

281 (1988). 

23. Atkinson, R., Aschmann, S. M., Arey, J., McElroy, P. A., and Winer, A. M. Environ. Sci. 

Technol. 23:243-244 (1989). 

24. Goodman, M. A., Aschmann, S. A., Atkinson, R., and Winer, A. M. Arch. Environ. Contam. 

Toxicol. 17:281-288 (1988). 
40

APPENDIX A. LITERATURE SEARCH RESULTS

Abbreviations and reference numbers are listed after the table.

Compound Name Chemical formula CAS # Sax 

Rating 

Carcinogen

 (1) (4) 

phosphorus (white) P4 7723-14-0 

phosphorus trioxide P2O3 1314-24-5 HR 3 

phosphorus pentoxide P2O5 1314-56-3 HR 3 

phosphine PH3 7803-51-2 HR 3 

phosphinic acid O=PH2(OH) 6303-21-5 HR 3 

phosphonic acid O=P(H)(OH)2 13598-36-2 HR 2 

orthophosphoric acid O=P(OH)3 7664-38-2 HR 3 

monomethyl phosphonic acid O=P(H)(OH)(CH3) 13590-71-1 HR 2 

dimethylphosphonate O=PH(OCH3)2 868-85-9 HR 3 suspected 

dimethyl phosphate O=P(OH)(OCH3)2 813-78-5 HR 1 

trimethyl phosphine P(CH3)3 594-09-2 HR 3 

trimethylphosphite P(OCH3)3 121-45-9 HR 2 suspected 

dimethyl methylphosphonate O=P(OCH3)2CH3 756-79-6 HR 2 questionable

trimethyl phosphate O=P(OCH3)3 512-56-1 HR 3 suspected 

trimethyl 2-phosphonoacrylate (CH3O)2P(O)C(=CH2)CO2CH3 55168-74-6 

Phosphonomycin O=P(OH)2(CHOCHCH3) 23155-02-4 HR 2 

diethylphosphonate O=PH(OC2H5)2 762-04-5 HR 2 

triethyl phosphine P(C2H5)3 554-70-1 HR 3 

triethyl phosphite P(OC2H5)3 122-52-1 HR 2 

di-(2-ethylhexyl) hydrogen phosphate O=P(OH)(OCH2CH(C2H5)(C3H8))2 298-07-7 

tris(2-ethylhexyl) phosphate O=P(OCH2CH(C2H5)(C4H9))3 78-42-2 suspect 

triethyl phosphate O=P(OCH2CH3)3 78-40-0 HR 2 

0-ethylpropyl phosphite P(OH)2OCH(CH3)(CH2CH2CH3) 

tris (2-ethylhexyl)phosphite P(OCH2CH(C2H5)(C4H9))3 301-13-3 HR 1 

propyl phosphonic acid O=P(OH)2((CH2)2CH3) 4672-38-2 

isopropyl phosphonate O=P(OH)2(OCH(CH3)2) 1623-24-1 HR 2 

diisopropylphosphonate O=PH(OCH(CH3)2)2 1809-20-7 HR 2 

diisopropyl methylphosphonate O=P(CH3)(OCH(CH3)2)2 1445-75-6 HR 2 

triisopropylphosphite O=P[CH(CH3)2]-[OCH(CH3)2]2 116-17-0 HR 3 

tributyl phosphine P((CH2)3CH3)3 998-40-3 HR 2 

Compound Name Chemical formula CAS # Sax 

Rating 

Carcinogen

 (1) (4) 

tributyl phosphinate O=P(C4H9)3 814-29-9 HR 3 

dibutylphosphate O=P(OH)(OC4H9)2 107-66-4 HR 2 

dibutylphosphonate O=PH(OC4H9)2 1809-19-4 HR 2 

tributyl phosphate O=P(O(CH2)3CH3)3 126-73-8 

triphenyl phosphine P(C6H5)3 603-35-0 HR 2 

triphenylphosphite O=P(C6H5)(OC6H5)2 101-02-0 HR 3 

triphenyl phosphate O=P(OC6H5)3 115-86-6 HR 3 

tricresyl phosphate O=P(OC6H5CH3)3 1330-78-5 no 

aka tritotyl phosphate (isomer mix) 78-30-8 

 563-04-2 

 78-32-0 

triisooctylphosphite O=P(CH2)5CH(CH3)2)(O(CH2)5CH(CH3)2)2 25103-12-3 HR 2 

tris(trimethylsilyl) phosphate O=P(OSi(CH3)3)3 10497-05-9 HR 2 

diethyl(2-(triethoxysilyl)ethyl)phosphonic acid O=P(OC2H5)2(CH2CH2Si(OC2H5)3) 757-44-8 HR 1 

ammonium phosphite (salt) P(OH)2ONH4 51503-61-8 HR 3 

ammonium dihydrogen phosphate O=P(OH)3 . NH3 7722-76-1 HR 2 

ammonium hydrogenphosphate O=P(OH)3 . 2NH3 7783-28-0 HR 2 

ammonium metaphosphate 

N-(phosphonomethyl)glycine aka "Glyphosate" O=P(OH)2CH2(NH)CH2C=O(OH) 1071-83-6 HR 3 

phosphonacetyl-l-aspartic acid O=P(OH)2(CHC(=O)NHCH(CO2H)CH2(CO2H)) 51321-79-0 HR 2 
41

0,S-dimethyl-N-acetylamido thiophosphate O=P(CH3O)(CH3S)(NHCOCH3) 30560-19-1 HR 3 

0,0-diethylthiophosphoryl-0-(cyanobenzaldoxime) S=P(OC2H5)2ON=C(C6H5)CN 

0,0-Di(2-ethylhexyl) dithiophosphoric acid S=P(SH)(OCH2CH(C2H5)(C4H9))2 5810-88-8 HR 2 

Bromophos S=P(OC6H2Cl2Br)(OCH3)2 2104-96-3 

phosphorus trichloride PCl3 7719-12-2 HR 3 

phosphorus oxychloride O=PCl3 10025-87-3 HR 3 

phosphorus tribromide PBr3 7789-60-8 HR 3 

2-chloroethyl phosphonic acid O=PH(OH)2((CH2)2Cl) 16672-87-0 

bis(trifluoromethyl)-chlorophosphine PCl(CF3)2 650-52-2 HR 3 

tris(2,3-dibromopropyl)phosphate O=P(OCH2CHBrCH2Br)3 126-72-7 suspected 

Compound Name European Risk and Safety Phrases (4) RTECS # Regulated Levels (4)

 (4) 

phosphorus (white) OSHA 0.1mg/kg 

phosphorus trioxide 

phosphorus pentoxide R35 S22-26 TH3945000 DFG MAK 1mg/m^3

phosphine EPA 200ppm 

phosphinic acid R34 S26-28-27-36/37/39 

phosphonic acid R34 S26-28-27-36/37/39 

orthophosphoric acid R34-22 S26-28-27-36/37/39 TB6300000 OSHA 1mg/m^3 

monomethyl phosphonic acid 

dimethylphosphonate R45-10-20/21/22-

36/37/38 

S53-16-44-36/37/39 SZ7710000 

dimethyl phosphate 

trimethyl phosphine R11-36/37/38 S16-26-36/37/39 

trimethylphosphite R10-34-20/21/22 S16-26-36/37/39-23 TH1400000 OSHA 2ppm 

dimethyl methylphosphonate R20/21/22-36/37/38-40 S23-44-26-36/37/39 SZ9120000 

trimethyl phosphate R45-46-20/21/22-

36/37/38 

S53-44-36/37/39-

3/7/9 

TC8225000 

trimethyl 2-phosphonoacrylate R36/37/38 S26-37/39 

Phosphonomycin 

diethylphosphonate 

triethyl phosphine R17-34 S16-27-26-36/37/39 

triethyl phosphite R10-36/37/38 S16-26-36/37/39-23 

di-(2-ethylhexyl) hydrogen phosphate TB7875000 

tris(2-ethylhexyl) phosphate MP0770000 

triethyl phosphate R22 S25 TC7900000 

0-ethylpropyl phosphite 

tris (2-ethylhexyl)phosphite 

propyl phosphonic acid R34 S26-28-27-36/37/39 TA0420000 

isopropyl phosphonate 

diisopropylphosphonate R36/37/38 S26-37/39 SZ7660000 

diisopropyl methylphosphonate 

triisopropylphosphite 

tributyl phosphine R17-34-20/21/22 S16-26-36/37/39-23 SZ3270000 

Compound Name European Risk and Safety Phrases (4) RTECS # Regulated Levels (4)

 (4) 

tributyl phosphinate R34-20/21/22 SZ1575000 

dibutylphosphate R36/37/38 S26-27-36/37/39 TB9605000 OSHA 1 ppm 

dibutylphosphonate R34 S26-27-36/37/39-23 HS6475000 

tributyl phosphate R22 S25 TC7700000 OSHA 0.2 ppm 

triphenyl phosphine R20/21/22-36/37/38 S26-36 SZ350000 

triphenylphosphite R22-36/38 S26-36 TH1575000 

triphenyl phosphate R20/21/22 S36 TC8400000 OSHA 3mg/m^3 
42

tricresyl phosphate R39/23/24/25 S20/21-28-44 TD0175000 

aka tritotyl phosphate 

 

triisooctylphosphite 

tris(trimethylsilyl) phosphate R10-34 S16-26-27-36/37/39 TC9700000 

diethyl(2-(triethoxysilyl)ethyl)phosphonic acid 

ammonium phosphite (salt) 

ammonium dihydrogen phosphate 

ammonium hydrogenphosphate R36/37/38 S26-36 

ammonium metaphosphate 

N-(phosphonomethyl)glycine aka "Glyphosate" R20/21/22-36/37/38 S26-36 MC1075000 

phosphonacetyl-l-aspartic acid 

0,S-dimethyl-N-acetylamido thiophosphate 

0,0-diethylthiophosphoryl-0-(cyanobenzaldoxime) 

0,0-Di(2-ethylhexyl) dithiophosphoric acid 

Bromophos 

phosphorus trichloride R34-37 S7/8-26 TH3675000 OSHA 0.2ppm 

phosphorus oxychloride R34-37 S7/8-26 TH4897000 OSHA 0.1 ppm 

phosphorus tribromide R14-34-37 S26 TH4460000 

2-chloroethyl phosphonic acid R36/37/38-23/24/25 S26-36 SZ7100000 

bis(trifluoromethyl)-chlorophosphine 

tris(2,3-dibromopropyl)phosphate 
43

Compound Name LD50 oral rat mg/kg Other Toxicology/ Information 

 

phosphorus (white) 3 (4) 

phosphorus trioxide highly toxic 

phosphorus pentoxide inh rat LC50=1217mg/m^3(1) 

phosphine Regulatory level is for extreme hazard (1) 

phosphinic acid corrosive, hygroscopic (4) 

phosphonic acid corrosive, hygroscopic (4) 

orthophosphoric acid 1530(1) 

monomethyl phosphonic acid 1740(1) irritant(1) 

dimethylphosphonate 3050(3) 

dimethyl phosphate 8714(1) 

trimethyl phosphine 

trimethylphosphite 1600(3) Severe eye,skin irritant (4) 

dimethyl methylphosphonate 8210(4) 

trimethyl phosphate 840(4) 

trimethyl 2-phosphonoacrylate irritant(4) 

Phosphonomycin intraperitoneal mouse LD50 4000mg/kg(1) 

diethylphosphonate 3900(3) skin-rabbit LD50=2165mg/kg(3) 

triethyl phosphine 

triethyl phosphite 3200(1) 

di-(2-ethylhexyl) hydrogen phosphate 4940(4) corrosive(4) 

tris(2-ethylhexyl) phosphate 37000(4) inhilation gpg LC50=450 mg/m^3(4) 

triethyl phosphate 1600(1) 

0-ethylpropyl phosphite 2300(5) plant growth regulator(5) 

tris (2-ethylhexyl)phosphite 10700(1) slightly toxic(1) 

propyl phosphonic acid 3723(5) plant growth regulator (5), corrosive, hygoscopic (4) 

isopropyl phosphonate corrosive(1) 

diisopropylphosphonate 3100(3) Mildly toxic via skin (3) 

diisopropyl methylphosphonate 826(1) 

triisopropylphosphite 167(3) 

tributyl phosphine 750(1) 

Compound Name LD50 oral rat mg/kg Other Toxicology/ Information 

 

tributyl phosphinate 

dibutylphosphate 3200(3) 

dibutylphosphonate 3200(3) severe eye irritant (3) 

tributyl phosphate 1400-3000(2) 

triphenyl phosphine 800(1) inhilation-rat LC50=1135ppm (1) 

triphenylphosphite 1600(3) 

triphenyl phosphate 3500-10800(2) 

tricresyl phosphate 1160-15800(2) 

aka tritotyl phosphate 

 

triisooctylphosphite 9200(3) moderately toxic via skin(3) 

tris(trimethylsilyl) phosphate 3440(1) moderately toxic (1) 

diethyl(2-(triethoxysilyl)ethyl)phosphonic acid 17200(1) 

ammonium phosphite (salt) inhilation-rat Lclo=580ppm(1) 

ammonium dihydrogen phosphate 5750(1) 

ammonium hydrogenphosphate low to moderate toxicity (1) 

ammonium metaphosphate 

N-(phosphonomethyl)glycine aka "Glyphosate" 470(1), >5000(2), 4873(4) herbicide (2) 

phosphonacetyl-l-aspartic acid human 862 mg/kg (nonlethal effects) 

0,S-dimethyl-N-acetylamido thiophosphate 866-945(5), 700(1) insecticide (5) 
44

0,0-diethylthiophosphoryl-0-(cyanobenzaldoxime) 2000(5) insecticide(5) 

0,0-Di(2-ethylhexyl) dithiophosphoric acid 4920(1) skin-rabbit LD50=1250mg/kg(1) 

Bromophos 3750-7700(2) pesticide, 0.4mg/kg human no adverse effect level(2) 

phosphorus trichloride 550(1), 18(4) inhilation rat LC50=104ppm (4 hr) (1) 

phosphorus oxychloride 380(1) 

phosphorus tribromide highly toxic (4) 

2-chloroethyl phosphonic acid 4220(5) plant growth regulator, inh rat LC50=90mg/kg x4hrs 

(5) 

bis(trifluoromethyl)-chlorophosphine 

tris(2,3-dibromopropyl)phosphate 1880-5240(2) 
45

Compound Name mp [deg C] bp [Deg C]/ Vap. Press Solubility in Water Flammability

 P [mm Hg] [mmHg] [mg/litre] 

phosphorus (white) yes (4) 

phosphorus trioxide 24 173(1) yes (1) 

phosphorus pentoxide 340(4) no (1) 

phosphine -132(4) -87(4) slightly (1) yes (1) 

phosphinic acid yes (1) 

phosphonic acid 

orthophosphoric acid 41(4) 158(4) 5@25C (4) yes (1) no (1) 

monomethyl phosphonic acid 

dimethylphosphonate 170(4) yes (4) 

dimethyl phosphate 

trimethyl phosphine -86(4) 38-39(4) yes (1) 

trimethylphosphite -78(4) 111(4) no (4) yes (4) 

dimethyl methylphosphonate 181(4) yes (1) 

trimethyl phosphate -46(4) 197(4) yes (1) 

trimethyl 2-phosphonoacrylate 91/0.1(4) 

Phosphonomycin 94(1) yes(1) 

diethylphosphonate 

triethyl phosphine 128(4) yes (1) 

triethyl phosphite 156(4) yes (1) 

di-(2-ethylhexyl) hydrogen phosphate -60(4) 

tris(2-ethylhexyl) phosphate 214(4) 

triethyl phosphate -56(1) 215(4) yes (1) yes (1) 

0-ethylpropyl phosphite liquid at ambient temperature (5) good (5) 

tris (2-ethylhexyl)phosphite 

propyl phosphonic acid 67(4) good (5) 

isopropyl phosphonate 

diisopropylphosphonate 73/10 (4) 

diisopropyl methylphosphonate 

triisopropylphosphite 

tributyl phosphine 150/50 (4) 

Compound Name mp [deg C] bp [Deg C]/ Vap. Press Solubility in Water Flammability

 P [mm Hg] [mmHg] [mg/litre] 

tributyl phosphinate 64-69(4) 150/1.5 (4) 

dibutylphosphate 

dibutylphosphonate 118/11 (4) 

tributyl phosphate -80(2) 150/10 (2) 9Pa@25C (2) 1012(4C), 2.85*10^-4(50C) (2) no (2) 

triphenyl phosphine 79(4) 377(4) no (1) yes (1) 

triphenylphosphite 23(4) 360, 150/0.1 (4) no (4) yes (4) 

triphenyl phosphate 49-50(4) 245/11 (4) 0.7-2.1 (2) yes(1), no (2)

tricresyl phosphate -33 (2) 241-255/4 (2) 0.35mg/litre (2) no (2) 

aka tritotyl phosphate 

 

triisooctylphosphite 

tris(trimethylsilyl) phosphate 3(4) 228/720 (4) yes (1) 

diethyl(2-(triethoxysilyl)ethyl)phosphonic acid 

ammonium phosphite (salt) 

ammonium dihydrogen phosphate 190(4) yes (1) 

ammonium hydrogenphosphate 155(1) yes (1) 

ammonium metaphosphate 

N-(phosphonomethyl)glycine aka "Glyphosate" 185(4) 10100 (2) no (1) 

phosphonacetyl-l-aspartic acid 

0,S-dimethyl-N-acetylamido thiophosphate 80(1) satisfactory (5) 
46

0,0-diethylthiophosphoryl-0-(cyanobenzaldoxime) 3(5) 102/0.01(5) 7mg/litre(5) 

0,0-Di(2-ethylhexyl) dithiophosphoric acid 

Bromophos 

phosphorus trichloride -118(1) 76(1) no (1) yes (1) 

phosphorus oxychloride 1(4) 105(4) 

phosphorus tribromide -40(1) 175(1) 

2-chloroethyl phosphonic acid 66(4) good (5) 

bis(trifluoromethyl)-chlorophosphine yes(3) 

tris(2,3-dibromopropyl)phosphate 5.5(2) 390(2) no(2) no(2) 
47

Compound Name Metal Compatibility [mils of penetration per year] (6) 

 <2 <50 >50 (incompatable) 

phosphorus (white) br (T<15), hast BCD, SS, nb, ni al, st, Cu br (T>20) 

phosphorus trioxide 

phosphorus pentoxide al, SS, hast BD hast C, Cu, st 

phosphine 

phosphinic acid 

phosphonic acid 

orthophosphoric acid hast B D(T<60)C, SS 304 hast BDG, SS, inc al, br, nb, st, Cu, ni 

monomethyl phosphonic acid 

dimethylphosphonate 

dimethyl phosphate 

trimethyl phosphine 

trimethylphosphite 

dimethyl methylphosphonate 

trimethyl phosphate 

trimethyl 2-phosphonoacrylate 

Phosphonomycin 

diethylphosphonate 

triethyl phosphine 

triethyl phosphite 

di-(2-ethylhexyl) hydrogen phosphate 

tris(2-ethylhexyl) phosphate 

triethyl phosphate 

0-ethylpropyl phosphite 

tris (2-ethylhexyl)phosphite 

propyl phosphonic acid 

isopropyl phosphonate 

diisopropylphosphonate 

diisopropyl methylphosphonate 

triisopropylphosphite 

tributyl phosphine 

Compound Name Metal Compatibility [mils of penetration per year] (6) 

 <2 <50 >50 (incompatable) 

tributyl phosphinate 

dibutylphosphate 

dibutylphosphonate 

tributyl phosphate al, SS, st, hast BC, ni 

triphenyl phosphine 

triphenylphosphite 

triphenyl phosphate 

tricresyl phosphate 

aka tritotyl phosphate 

 

triisooctylphosphite 

tris(trimethylsilyl) phosphate 

diethyl(2-(triethoxysilyl)ethyl)phosphonic acid 

ammonium phosphite (salt) 

ammonium dihydrogen phosphate 

ammonium hydrogenphosphate hast B, SS 304,400 nb, hast C, inc, SS 316 al, br, st 

ammonium metaphosphate al, st, hast, inc, ni, SS Cu, br 

N-(phosphonomethyl)glycine aka "Glyphosate" 

phosphonacetyl-l-aspartic acid 
48

0,S-dimethyl-N-acetylamido thiophosphate 

0,0-diethylthiophosphoryl-0-(cyanobenzaldoxime) 

0,0-Di(2-ethylhexyl) dithiophosphoric acid 

Bromophos 

phosphorus trichloride st hast C, inc, ni al, Cu 

phosphorus oxychloride al, hast BC, inc, ni st, br 

phosphorus tribromide 

2-chloroethyl phosphonic acid 

bis(trifluoromethyl)-chlorophosphine 

tris(2,3-dibromopropyl)phosphate 
49

Index Key for Toxicology and Materials Compatibility Data on PhosphorusContaining Compounds

Sources: 

(1) Sax, N. I., and Lewis, R. J., “Dangerous Properties of Industrial Materials”, 7th

ed., Van Nostrand Reinhold, New York, 1989. 

(2) World Health Organization, “Organophosphorus Insecticides: A General 

Introduction”, Environmental Health Criteria, Vol 63, Finland, 1986. 

World Health Organization, “Phosphine and Selected Metal Phosphides”, 

Environmental Health Criteria, Vol 73, Finland, 1988. 

World Health Organization, “Tricresyl Phosphate”, Environmental Health 

Criteria, Vol 110, Finland, 1990. 

World Health Organization, “Triphenyl Phosphate”, Environmental Health 

Criteria, Vol 111, Finland, 1991. 

Mensink, H., Janssen, P., World Health Organization, “Glyphosate”, 

Environmental Health Criteria, Vol 159, Finland, 1994. 

van Esch, G. J., World Health Organization, “Tris (2,3-dibromopropyl) phosphate 

and Bis(2,3-dibromopropyl) phosphate”, Environmental Health Criteria, Vol 173, 

Finland, 1988. 

(3) Kaizerman, J. A., Tapscott, R. E., “Advanced Streaming Agent Development, 

Volume III: Phosphorus Compounds”, NMERI 96/5/32540, 1996 

(4) Lenga, R.E., Votoupal, K. L. eds, “The Sigma-Aldrich Library of Regulatory and 

Safety Data”, Milwaukee, WI, 1992. 

(5) Mel’nikov, N. N., “Organic Compounds of Phosphorus”, Joint Publications 

Research Service, Arlington, VA, 1975. 

(6) Schweitzer, P.A., “Corrosion Resistance Tables”, 3rd ed, rev. and expanded, 

Dekker, New York, 1991
European Risk and Safety Phrases (Ref. 4 above) Code Phrase R10 Flammable R11 Highly flammable R14 Reacts violently with water R17 Spontaneously flammable in air R20/21/22 Harmful by inhalation, in contact with skin and if swallowed R22 Harmful if swallowed R23/24/25 Toxic by inhalation, in contact with skin and if swallowed R34 Causes burns R35 Causes severe burns R36/37/38 Irritating to eyes, respiratory system and skin R36/38 Irritating to eyes and skin R37 Irritating to respiratory system R39/23/24/25 Toxic: danger of very serious irreversible effects through inhalation, in contact with skin and if swallowed R40 Possible risks of irreversible effects R45 May cause cancer R46 May cause heritable genetic damage S3/7/9 Keep container tightly closed in a cool, well ventilated place S7/8 Keep container tightly closed and dry S16 Keep away from sources of ignition - No smoking S20/21 When using do not eat, drink or smoke S22 Do not breathe dust S23 Do not breathe vapour S25 Avoid contact with eyes S26 In case of contact with eyes, rinse immediately plenty of water and seek medical advice S27 Take off immediately all contaminated clothing S28 After contact with skin, wash immediately with plenty of water S36 Wear suitable protective clothing S36/37/39 Wear suitable protective clothing, gloves and eye/face protection S37/39 Wear suitable gloves and eye/face protection S44 If you feel unwell, seek medical advice (show the label where possible) S53 Avoid exposure - obtain special instructions before use 
51

Abbreviations used in Materials Compatibility Listings 

Metals:

ss-Stainless Steel 

br-Brass 

al-Aluminum 

hast-Hastelloy 

ni-Nickel 

cu-Copper 

st-Carbon Steel 

nb-Naval Bronze 

inc-Inconel 

Nonmetals:

tfn-Teflon 

pvc-Polyvinyl Chloride 

rub-Natural Rubber 

pyr-Pyrex 

kal-Kalrez 

bn-Buna-N 

v-Viton 

c-Carbon 

epx-Epoxy 

si-Silicon Rubber