Metal alkyls and their solutions

Transcription

1 Metal alkyls and their solutions Burning properties Introduction AkzoNobel supplies a wide range of metal alkyls and their solutions to the olefin polymerization and other industries. The principal ones are based on aluminum. These potentially hazardous products are transported under a nitrogen blanket in specially designed portable tanks. Metal alkyls are used either as the neat product or as solution in hydrocarbons. Commonly used solvents for such solutions are isopentane, n-pentane, n-hexane and n-heptane. Safe handling of metal alkyls and their solutions during unloading and application is of high priority at all times. Despite the precautions taken, an accidental spillage of metal alkyl may occur. In the event the metal alkyl is accidentally exposed to the air, immediate reaction with oxygen occurs and this may lead to ignition and fire. The fire generated by a pool of metal alkyl liquid may endanger people and process equipment. In an extensive research program, including literature study and experimental work, the AkzoNobel Safety Laboratory (Deventer, The Netherlands) has studied the burning properties of aluminum alkyls. The following aspects have been taken into consideration: the burning rate of the fire the height of the flames the thermal radiation emitted from the fire. This technical bulletin provides information about the burning properties of neat aluminum alkyl and aluminum alkyl solution pool fires. Furthermore, it compares the burning properties of neat aluminum alkyls with those of commonly used hydrocarbon solvents and shows the contribution of the hydrocarbon solvents on the burning properties of the aluminum alkyl solutions Overall, this bulletin can contribute to a more thorough assessment of the potential risks associated with the use of neat aluminum alkyls and their solutions. Page 1 of 24

2 Freely burning pool fires In the event of an accidental spill of metal alkyl a layer of liquid will be formed (depending on the quantity and the surface on which the spill occurs). If this layer ignites, the burning liquid can best be compared with a freely burning pool fire. Generally, a freely burning liquid pool fire can be divided into three zones namely, the fuel zone, the combustion zone (fire) and the plume zone (smoke) [1]. A schematic diagram of a liquid pool fire with the various zones is shown in Figure 1. Figure 1. A schematic diagram of a pool fire with the various zones [1] plume thermal radiation visible flameheight combustion zone fuel vapor air fuel During a pool fire it is assumed that the fuel will evaporate from the surface at the boiling point of the liquid, while the bulk of the liquid remains at a lower temperature. As the fuel vapor rises, it sucks in the surrounding air and burns in the combustion zone. Part of the heat generated in this zone is transferred back to the fuel surface where it is used to evaporate more fuel and thus keep the fire burning. The rest of the combustion heat is partly dispersed to the environment as thermal radiation and partly transferred to the plume zone. The plume zone consists of a mixture of all combustion products generated by the pool fire, including solid and liquid particles and hot gases. Page 2 of 24

3 Burning properties It is important to first consider some theoretical aspects involved with the burning properties (burning rate, flame height and thermal radiation) of freely burning pool fires. Burning rate The burning rate of fuels can be expressed as burning velocity (in m/s) and mass burning rate (in kg/m 2.s) for single component fuels and blended fuels. The characteristics of both types of fuel are described below. Single component fuels It is known from literature that all single component fuels such as hydrocarbon solvents show the same general relationship between the burning velocity (m/s) and the pool diameter (m) [2,4], see Figure 2. The burning velocity first decreases with increasing pool diameter, with an almost constant product of the two. This is the laminar flow region with Reynolds numbers less than 20. The Reynolds number is based on the properties of the upward flow of non-burning vapor leaving the pan. With further increases of the pool diameter, the burning velocity begins to increase. The sharp rise in the burning rate occurs in the range of Reynolds numbers of 20 to 200 (transition range). The burning velocity levels off at a Reynolds number of about 500. This corresponds with a pool diameter of about 1 meter. Above that value, the burning of the fire is turbulent and its burning velocity is substantially uninfluenced by the pool diameter or the fuel type. Figure 2. General relationship between the burning velocity and the pool diameter for some oil components [2,4] Page 3 of 24

4 Blended fuels For blended fuels, an extra dimension of burning behavior needs to be considered. Blended fuels, especially those whose components differ widely in their volatility (such as hydrocarbon diluted metal alkyl solutions), do not burn at a uniform rate. Initially, the burning rate is characteristic of the most volatile component (hydrocarbon solvent). During the middle portion of burning, the less volatile component (neat metal alkyl) must be brought to the boiling point of the blend. Finally, as the fractionation proceeds, the burning rate becomes characteristic of the higher boiling fraction. Thus, the burning rate of a blend will be maximum in the beginning and gradually decrease to lower values as burning proceeds. Relation between burning rate and thermochemistry of the fuel Based on extensive burning rate measurements, Burgess and Zabetakis [3] proposed the following correlation for liquid hydrocarbon pool fires: V = (ΔH c / ΔH v * ) (1) where, V = the maximum burning velocity ΔH c = the net heat of combustion ΔH * v = the modified heat of vaporization (m/s) (kj/mole) (kj/mole) If the ratio ΔH c /ΔH * v is high, more heat (that is heat of combustion (exothermic) minus heat of vaporization (endothermic)), is available to warm up the liquid surface towards the boiling point and to increase the mass flow of vapor into the combustion zone. The mass burning rate (in kg/m 2.s) can be determined by multiplying the burning velocity [m/s] with the liquid fuel density. Using 790 kg/m 3 as an average density, the correlation for the mass burning rate for hydrocarbons becomes as follows [3]: m = 10-3 (ΔH c / ΔH v * ) (2) where, m = the maximum mass burning rate [kg/(m 2.s)] Page 4 of 24

5 Flame height The height of the flame is dependent on the pool diameter and the mass burning rate. Thomas [4] has developed a correlation for the mean visible height of turbulent diffusion flames in both the absence and the presence of wind. The correlation in the absence of wind is as follows: H D = 42 ( ρ a m ) g D 0.61 (3) where, m = the mass burning rate of the fuel [kg/(m 2.s)] ρ a = the ambient air density [1.29 kg/m 3 ] g = the gravitational constant [9.81 m/s 2 ] D = the diameter of the pool [m] The presence of wind can, especially in open surroundings, deform the shape of the vertical flame. It has been observed that a 7 m/s wind measured on open ground reduces rapidly within the confines of a plant with equipment spaced at normal distances, and is reduced to approximately 2 m/s at ground level within 5 to 10 meter of the plant periphery. With a steady air stream of 2 m/s the vertical flame is deformed to an angle of 45 (flame tilt); at the same time, it has been observed that the flame on the upstream side of the fire hugs the ground for a distance of approximately half a pool diameter before it rises from the ground (flame drag), see Figure 3. Figure 3. Influence of the wind velocity on the shape of the flame Wind Flame tilt 45 Flame drag D ½ D Page 5 of 24

6 Thermal radiation A common approach to evaluate the thermal radiation field around a fire is based on recognizing the fact that the radiation originates from the hot products of combustion. This approach is called solid flame radiation model [4,5]. In the solid flame radiation model, the entire visible volume of the flame emits thermal radiation. The flame is assumed to be a cylinder with a diameter equal to the base diameter of the flame and an axial length equal to the length of the visible fire plume. The non-visible part of the flame does not contribute significantly to the thermal radiation emitted [6]. The flame is assumed to radiate uniformly over the entire surface of the cylinder. Using this model, the thermal radiation intensity (I) received from the fire is given by the following equation: I = τ x F x E (4) where, τ = the atmospheric transmissivity [-] F = the geometric view factor [-] E = the average emissive power of the flame [W/m 2 ] The atmospheric transmissivity (τ) Atmospheric attenuation is the consequence of absorption of radiation by the medium present between radiator (fire) and radiated object (observer). For thermal radiation, atmospheric absorption is primarily due to water vapor and, to a lesser extent, to carbon dioxide. τ = 1 - α water - α carbon dioxide (5) The geometric view factor (F) The geometric view factor is the ratio between the received and the emitted radiation energy per unit area (of the receiver and the radiator respectively), for complete transmission. This factor is determined by the dimensions and the shape of the flame, and the location and orientation of the receiving subject. By assuming some simple radiator shapes such as a cylinder, formulas for the view factor are obtained for use in practice. Actual fires are often cylindrical, or can be treated as such by an appropriate adjustment of the dimensions. Page 6 of 24

7 The emissive power of a flame (E) The emissive power is the total radiative power leaving the surface of the fire per unit area per unit time. The emissive power can be calculated according Planck's law of radiation and with the heat of release rate. The Planck's law of radiation is used to calculate the emissive power of the flame with the flame temperature, see equation 6. The flame temperature is determined with an infra red temperature meter, the Comet The emissive power using heat of release rate is used to calculate the fraction radiant heat (f), see equation 7. The fraction radiant heat is the fraction of the combustion energy radiated to the surroundings. For different pool fires the value f usually varies from 0.15 to 0.40 [5]. A short description of Planck's law of radiation and the heat of release rate is provided below. Planck's law of radiation The emissive power of a flame is mainly determined by the temperature of the combustion products in the visible part of the flame. The Stefan-Boltzman law says that the rate of emission of a black radiator is proportional to the 4 th power of the flame absolute temperature. Since, the flame is not always a black radiator, its rate of emission becomes smaller. The flame emissive power can be approximated by [7]: E = ε x σ x (T 4 f - T 4 a) (6) where, ε = the emissivity ( 0 < ε < 1 ) (-) σ = the Stefan-Boltzmann constant ( ) (kw/[m 2.K 4 ]) T a, T f = the ambient and flame temperature (K) The heat of release rate: The emissive power of a flame can also be measured [8] using the heat release rate by : E = f x m x ΔH c x A pool / A (7) where, f = the fraction of radiant heat (-) m = the maximum mass burning rate (kg/[m 2.s]) ΔH c = the heat of combustion (kj/kg) A pool = the pool fire area (m 2 ) A = the emissive area (m 2 ) Page 7 of 24

8 Criteria for thermal radiation hazards This section gives some reference values of thermal radiation intensity in order to prevent hazards for exposed personnel and equipment, due to a pool fire. Effect on personnel and equipment The thermal radiation from a pool fire may cause pain, burns on unprotected skin or even fatal injury if the intensity of radiation is of sufficient duration. The effect is a function of thermal radiation intensity, duration of exposure and factors involving human response, age and protection afforded by clothing. In Figure 4 pain, injury and fatality levels are shown for thermal radiation as a function of the exposure time. The highest heat-flux that the skin can absorb during a long time without feeling pain is about 1.0 kw/m 2. This value is in the range of the heat flux received from a mid day sunshine in summertime (30 C). Figure 4. Pain, injury and fatality levels for personnel resulting from thermal radiation as a function of exposure time [9] Time (s) Pain threshold Injury threshold 1% Fatality 50% Fatalities 100% Fatalities Thermal radiation intensity (kw/m ) Personnel wearing protective equipment while handling aluminum alkyls [12] are for some time protected against high radiation levels from an accidental fire and thereby prevent immediate burns on their body. Page 8 of 24

9 This protective effect of clothing is dependent on various factors: the aluminum layer on the suit has good reflective properties so the heat can only penetrate to a limited extent air layers between various pieces of clothing (for instance aluminized suit and coverall) and between clothing and skin substantially improve the resistance to heat furthermore, all fabrics used are to a certain degree non-ignitable, e.g. PBI (polybenzimidazole), aramid fibre and cotton. In most cases, buildings, tanks and process equipment can safely tolerate higher degrees of heat density than defined for personnel. However, if anything vulnerable to overheating is involved, such as construction materials that have low melting points (for example, aluminum or plastic), heat sensitive process streams, flammable vapor spaces, or electrical equipment, then the effect of radiant heat may need to be evaluated. Some thermal radiation damage levels are mentioned in Table 1. Table 1. Thermal radiation damage levels for personnel and equipment [10] Thermal radiation intensity (kw/m 2 ) Effect Personnel: Minimum value necessary to be felt as pain after 1 minute of skin exposure Personnel: Causes pain after seconds exposure, injury after 30 seconds exposure Buildings: Exposed wood and flammable vapors released by insulation material could be ignited Tanks, equipment and structures: Thin, uninsulated steel can lose mechanical integrity Page 9 of 24

10 Burning experiments AkzoNobel performed several experiments to investigate the burning properties of neat aluminum alkyls, aluminum alkyl solutions and hydrocarbon solvents. Because of its commercial importance triethylaluminum (TEAL) was studied in neat (100%) form and as solution in isopentane and n-hexane. Diethylaluminum chloride (DEAC) and ethylaluminum sesquichloride (EASC) were studied in neat form. Experimental set-up In the experimental work, neat aluminum alkyls, aluminum alkyl solutions and hydrocarbon solvents were burned separately. The fuel was contained in a stainless steel pan of one square meter. The pan was placed on a weighing device and insulation material was placed between the pan and weighing device. The weighing device measured the weight loss versus time. In the case of aluminum alkyl experiments, before actually starting the dosing of alkyl, a stainless steel cover was placed on the pan and the volume purged with nitrogen. This is done to prevent an early start of the fire during dosing. The aluminum alkyls and their solutions were dosed from a pressurized 20 liter cylinder via a copper tube into the pan. When the cover was removed, the product came into contact with air and ignited spontaneously or was ignited by a micro flame. The hydrocarbon solvents were dosed directly from a can into the pan and ignited by a micro flame. The thermal radiation intensity was determined directly with a radiometer (thermopile CA-1) at 24 meter distance from the center of the fire and indirectly (via the temperature) with an infra red temperature meter (Comet 1000). It was decided to place the radiometer at 24 meters because the whole fire is then observed (Total View) and at that distance the amount of radiation received is within the output range of the thermopile. Furthermore, to exclude influences of the wind on the measured signal, the radiometer is placed upwind. The Comet functions independently of distance and is for practical reasons installed near the radiometer. A few meters from the fire, a video camera was installed in order to record the burning experiments. The position of the video camera was perpendicular to the thermopile for correct determination of the tilt angle of the fire. An overview of the equipment used for the experiments is shown in Figure 5. Page 10 of 24

11 Figure 5. Experimental set-up of burning experiment LATERAL VIEW Comet Sensor Recorder 1m Balance 24m TOP VIEW Recorder Sensor Comet Wind 1m Balance Videocamera Results and discussion Burning rate These burning experiments confirmed that for single component fuels (such as neat metal alkyls and hydrocarbon solvents) the burning rate becomes constant and maximum for pool diameters larger than one meter, see Figure 6. This is in line with the theory on the relationship between burning velocity and pool diameter, described on pages 3 and 4. Page 11 of 24

12 Figure 6. Comparison of the relation between burning velocity and pool diameter for neat TEAL and oil components υ, LIQUID BURNING VELOCITY, mm/min DIESEL OIL GASOLINE TRACTOR KEROSINE TEAL LAM INAR FLOW REGIM E TRANSITION TURBULENT FLOW REGIM E PAN DIAMETER, CENTIMETERS (d) The maximum mass burning rate of the neat aluminum alkyls, aluminum alkyl solutions and hydrocarbons are compiled in Tables 2 and 3, and graphically depicted in Figure 7. Aluminum alkyls It appeared that the maximum mass burning rate of all neat aluminum alkyls is not exceptionally high, and in general even lower than hydrocarbon solvents. For example: The mass burning rate of isopentane (0.103 kg/m 2.s) is more than three times higher than that of neat TEAL (0.029 kg/m 2.s) The mass burning rate of n-hexane (0.077 kg/m 2.s) is twice as high as that of neat DEAC (0.039 kg/m 2.s). Page 12 of 24

13 Table 2. The maximum mass burning rates of the neat aluminum alkyls and hydrocarbon solvents Product Neat DEAC Neat EASC Neat TEAL Isopentane n-pentane n-hexane n-heptane Maximum mass burning rate (kg/m 2.s) Aluminum alkyl solutions An aluminum alkyl solution is simply a mixture of two components, a hydrocarbon solvent and an aluminum alkyl. The overall burning rate of such a mixture is determined by the rate of evaporation of the two components in the combustion zone. Because of their difference in volatility the evaporation rate of a hydrocarbon solvent is much higher than that of an aluminum alkyl. This phenomenon was clearly recognized during the fire experiments. Aluminum alkyl solutions showed a maximum burning rate in the beginning (due to the burning of the solvent) and a lower burning rate as the burning continued. The mass burning rate data for TEAL/isopentane and TEAL/n-hexane solutions are given in Table 3. Table 3. The maximum mass burning rates of aluminum alkyl solutions for first and second part of burning period Product 11% TEAL/Isopentane 22% TEAL/Isopentane 20% TEAL/n-Hexane 50% TEAL/n-Hexane Maximum mass burning rate (kg/m 2.s) Page 13 of 24

14 Figure 7. Comparison of mass burning rate of neat metal alkyls, metal alkyl solutions and hydrocarbon solvents 50% TEAL/n-Hexane 20% TEAL/n-Hexane 22% TEAL/Isopentane 11% TEAL/Isopentane n-heptane n-hexane n-pentane Isopentane neat TEAL neat EASC neat DEAC Mass burning rate (kg/m.s) In Figure 8 the above mentioned phenomena are shown for 11 and 22% solutions of TEAL in isopentane. It is observed for both solutions that during the first 180 seconds the weight decrease per second (slope of the curve) approaches that of isopentane. During the middle portion of burning ( s) the weight decrease per second gradually reduces. After 260 seconds the weight decrease per second for both solutions is similar to that of neat TEAL. Figure 8. Contribution of isopentane and TEAL to the overall burning rate of the TEAL/isopentane solutions Weight decrease (kg) Time (s) neat TEAL Isopentane 11% TEAL/isopentane 22% TEAL/isopentane Page 14 of 24

15 As has been shown in the introduction, the ratio of heat of combustion to modified heat of vaporization gives a good indication of the burning rate one can expect for a liquid pool fire. The mass burning rates of neat metal alkyls fall within the range found for hydrocarbons studied by Burgess & Zabitakis [4], such as hexane, benzene or gasoline. See Figure 9. However, the values for TEAL, DEAC and EASC are all somewhat lower than predicted. This may be caused by the fact that the heat of combustion used in our calculations [14] is higher than the experimental value due to incomplete combustion that occurs under the practical conditions of our tests. Figure 9. Relationship between mass burning rate and thermochemistry of the fuel according to Burgess & Zabitakis [4] M ASS BURNING RATE (kg/m 2 s) Δ H c / ΔH * v EASC JP4 BENZENE XYLENE HEXANE GASOLINE DEAC LNG LPG BUTANE METHANOL TEAL H c / H * Δ Δ v Page 15 of 24

16 Visible flame height Flame heights were measured during our burning rate experiments. The visible flame heights determined for the neat aluminum alkyls are much lower than those for the hydrocarbon solvents. For example, for these 1 m 2 pool fires: The flame height of isopentane (4.0 m.) is twice as high as that of neat TEAL (2.0 m) The flame height of n-hexane (3.1 m.) is 35 percent higher than that of neat DEAC (2.3 m). The following pictures show the difference in flame height between a neat TEAL and an 11% TEAL/ isopentane pool fire. It can be clearly observed that the flame height of the 11% solution is much higher (right), in the first part of the burning process, than for the neat TEAL (left). In Table 4 the measured and calculated flame heights are compared for various 1 m 2 pool fires. The difference between the measured and calculated value can be explained by the fact that on larger scale the visible flame height is difficult to measure since the flame is never steady. Not even at ideal wind conditions. Wind and flame pulsation will both deform the shape of the flame. Also the generation of smoke makes it difficult to determine visually the end of the combustion zone and the beginning of the smoke plume. Page 16 of 24

17 Table 4. Comparison of measured and calculated flame heights for 1 m 2 pool fires Product Measured (m) Calculated (m) DEAC EASC TEAL Isopentane n-pentane n-hexane n-heptane In Figure 10 the calculated visible flame heights of neat metal alkyl and hydrocarbon solvent pool fires are shown for larger pool surfaces using the Thomas correlation (see equation 3). Figure 10. Calculated visible flame heights of neat aluminum alkyl and hydrocarbon solvent pool fires for larger pool surfaces Calculated visible flame height (m) Pool surface (m 2 ) Isopentane n-hexane n-heptane DEAC TEAL As can been seen from the pictures and the measured/calculated flame heights, the visible flame heights of neat aluminum alkyls are much lower than those for hydrocarbon solvents. Page 17 of 24

18 Thermal radiation The thermal radiation emitted by our 1 m 2 pool fires was determined directly with the thermopile CA-1. Moreover, it was measured indirectly with the Comet 1000 via the temperature using Planck's law (equation 6). In Figure 11 the results obtained with the thermopile are given for neat TEAL, 22% TEAL/isopentane and isopentane pool fires. In Figure 12 the results with the Comet 1000 are given for the same pool fires. Both figures show the same trend. The flame temperature and thus the thermal radiation received from the isopentane fire is much higher than that from the neat TEAL fire. For the 22% solution of TEAL in isopentane, the flame temperature and the thermal intensity are in the beginning characteristic for isopentane (bp=28 C) and at the end characteristic for TEAL (bp=187 C). It is clearly shown that during the first 140 seconds the temperature and the thermal intensity approach those of isopentane. During the middle portion of burning ( s) the temperature and thermal intensity gradually decrease. After 240 seconds the flame temperature and thermal intensity are similar to those for neat TEAL. Figure 11. The measured thermal radiation intensity (24 meters from the fire) versus the burning time for neat TEAL, 22% TEAL/Isopentane and pure isopentane pool fires Thermal radiation (W/m 2 ) Isopentane neat TEAL 22% TEAL/isopentane Time (s) Page 18 of 24

19 Figure 12. The measured flame temperature versus the burning time for neat TEAL, 22% TEAL/ Isopentane and pure isopentane pool fires Temperature (K) Isopentane neat TEAL 22% TEAL/isopentane Time (s) The results from the 1 m 2 burning experiments can be used to calculate radiation intensities of large fires at different distances. Figures 13, 14 and 15 show the calculated relation between the thermal intensity and the distance from the center of the fire for 1, 5, 10 m 2 pool fires of neat TEAL, isopentane and n-hexane. Figure 13. Relation between the thermal radiation intensity and the distance from the center of the fire for a 1 m 2 pool fire of neat TEAL, isopentane and n-hexane Thermal radiation (kw/m 2 ) Distance from the fire (m) TEAL n-hexane isopentane Page 19 of 24

20 Figure 14. Relation between the thermal radiation intensity and the distance from the centre of the fire for a 5 m 2 pool fire of neat TEAL, isopentane and n-hexane Thermal radiation (kw/m 2 ) Distance from fire (m) TEAL n-hexane isopentane Figure 15. Relation between the thermal radiation intensity and the distance from the centre of the fire for a 10 m 2 pool fire of neat TEAL, isopentane and n-hexane Thermal radiation (kw/m 2 ) Distance from fire (m) TEAL n-hexane isopentane When the thermal intensity emitted by a burning fuel is known as a function of the distance, safety distances for personnel as well as equipment and buildings can be determined using the thermal radiation damage levels [9,10]. In Table 5 and 6 the distances from the fire where the thermal radiation received corresponds with the thermal radiation damage levels (introduced on pages 8 and 9) are given for 1, 5 and 10 m 2 pool fires of neat TEAL and isopentane. The values are derived from Figures 13, 14 and 15. Page 20 of 24

21 Table 5. The distances from a 1, 5 and 10 m 2 neat TEAL fire where the thermal radiation received corresponds with the thermal radiation damage levels for personnel and equipment Thermal radiation damage levels (kw/m 2 ) Effect on personnel and equipment Personnel: Highest heat flux on skin during long period without feeling pain Personnel: Min. value to be felt as pain after 1 minute exposure of skin Personnel: Pain after seconds exposure and injury after 30 seconds Buildings: Exposed wood and flammable vapors could be ignited Tanks, equipment: Thin, uninsulated steel can lose mechanical integrity Distance (m) from pool fire with surface of 1 m 2 5 m 2 10 m Table 6. The distances from a 1, 5 and 10 m 2 isopentane fire where the thermal radiation received corresponds with the thermal radiation damage levels for personnel and equipment Thermal radiation damage levels (kw/m 2 ) Effect on personnel and equipment Personnel: Highest heat flux on skin during long period without feeling pain Personnel: Min. value to be felt as pain after 1 minute exposure of skin Personnel: Pain after seconds exposure and injury after 30 seconds Buildings: Exposed wood and flammable vapors could be ignited Tanks, equipment: Thin, uninsulated steel can lose mechanical integrity Distance (m) from pool fire with surface of 1 m 2 5 m 2 10 m The data above show which distances have to be taken into account to prevent thermal radiation damage to personnel (pain or injury) and to equipment (mechanical integrity). Page 21 of 24

22 Personnel, not wearing any protective clothing, should stay at least 9, 14, 18 meters away from respectively a 1, 5, 10 m 2 pool fire of neat TEAL. In case of an isopentane fire personnel should at least stay twice as far away from the fire. The safety distances for buildings and equipment are quite short, which means that real thermal radiation damage will only occur when buildings or equipment are really close to the fire and exposed for a longer period of time. Conclusions Neat aluminum alkyls burn slower than aluminum alkyl solutions. The flame height as well as the thermal radiation emitted to the surroundings are much lower for neat aluminum alkyls than for aluminum alkyl solutions. Neat aluminum alkyls are single component fuels, which burn uniformly and therefore show a constant burning rate, flame height and thermal radiation during the complete fire period. Aluminum alkyl solutions are blended fuels containing a fraction of hydrocarbon solvent. The difference in thermochemistry (e.g. heat of combustion, heat of evaporation and physical properties (e.g. boiling point) of the aluminum alkyl and hydrocarbon solvent determine the overall burning characteristics of the aluminum alkyl solution. The burning rate, flame height and thermal radiation data in this bulletin make it possible to estimate the impact of fires involving aluminum alkyls. The decision whether to use a neat aluminum alkyl or an aluminum alkyl solution as co-catalyst in a polymerization (or other) process is often a complex one. In addition to safety aspects, factors like suitability for the application and compatibility with process conditions play a role. Environmental, logistic and economical aspects are also to be considered. We hope that this information contributes to a more thorough understanding of the risks associated with the use of neat aluminum alkyls and their dilutions. AkzoNobel personnel will be pleased to provide any guidance on this subject via the responsible AkzoNobel representative. Page 22 of 24

23 Additional remarks With the knowledge presented in this bulletin proper preventive measures can be taken or decisions can be made at each stage of the fire to minimize the damage to the surroundings. The scheme below shows the different stages of an accidental metal alkyl exposure to the atmosphere and indicates where preventive measures can be taken. Reference is made to several detailed AkzoNobel technical bulletins, which describe aspects of the safe use of aluminum alkyls. Neat aluminum alkyl or aluminum alkyl solution spill occurs Preventive measures: Amount of aluminum alkyl spilled Fail-safe shutdown system [11] Immediate or delayed self-ignition Pool fire Reduce surface with e.g. containment walls, sloping Burning rate Flame height Thermal radiation Effect on surroundings Personnel:protective clothing [12] Equipment: safety distances, fire walls cool facilities Minor damage Major damage Let fire burn itself out! Control with extinguishing agent [13] Page 23 of 24

24 References 1. Burgess D.S., Strasser A. and Grumer J., Diffusive Burning of Liquid Fuels in Open Trays, U.S. Bureau of Mines, Pittsburgh, Pennsylvania. 2. Blinov V.I. and Khudiakov G.N. (Reviewed by H.C. Hottel), Certain Laws governing Diffusive Burning of Liquids, Academy of Science, USSR, Burgess D.S. and Zabetakis M.G., Fire and Explosion Hazards Associated with LNG, US Bureau of Mines Report, 6099, Mudan K.S., Thermal Radiation Hazards from Hydrocarbon Pool Fires, Prog. Energy Combustion Sci, 1984, Vol.10, pp Croker W.P. and Napier D.H. Thermal Radiation Hazards of Liquid Pool Fires and Tank Fires, I.CHEM.E. Symposium Series, No Markstein G.H., Radiative Energy Transfer from Turbulent Diffusion Flames Combust. Flame, 27, pp.51-63, Hottel H.C. and Sarofim A.F., Radiative Transfer, McGraw Hill, New York, Mudan K.S., Geometric View Factor for Thermal Radiation Hazards Assessment, Fire Safety Journal, vol.12, pp , Eisenberg N.A. et al., Vulnerability Model, A simulation system for assessing damage resulting from marine spills, NTIS AD-AO15-245, Springfield, VA (1975). 10. Bagster D.F. and Pitlado R.M., Thermal Hazard in the Process Industry, Chemical Engineering Progress, pp , July AkzoNobel Technical Bulletin, Fail-safe shutdown system (MA ). 12. AkzoNobel Technical Bulletin, Operator protection during handling metal alkyls (MA ). 13. AkzoNobel Technical Bulletin, Control of metal alkyl fires (MA ). 14. AkzoNobel general brochure, Metal Alkyls (1995). All information concerning this product and/or suggestions for handling and use contained herein are offered in good faith and are believed to be reliable. AkzoNobel Polymer Chemicals, however, makes no warranty as to accuracy and/or sufficiency of such information and/or suggestions, as to the product's merchantability or fitness for any particular purpose, or that any suggested use will not infringe any patent. Nothing contained herein shall be construed as granting or extending any license under any patent. Buyer must determine for himself, by preliminary tests or otherwise, the suitability of this product for his purposes. The information contained herein supersedes all previously issued bulletins on the subject matter covered. The user may forward, distribute, and/or photocopy this document only if unaltered and complete, including all of its headers and footers, and should refrain from any unauthorized use. You may not copy this document to a website. Akzo Nobel Polymer Chemicals B.V. Akzo Nobel Polymer Chemicals LLC Akzo Nobel (Asia) Co., Ltd. Amersfoort, The Netherlands Chicago, U.S.A. Shanghai, PR China Tel Tel Tel Fax (Toll free US only) Fax Fax [email protected] [email protected] [email protected] AkzoNobel Polymer Chemicals Page 24 of 24