US20070289658A1

US20070289658A1 - Method of filling containers with gases

Info

Publication number: US20070289658A1
Application number: US11/452,023
Authority: US
Inventors: Fred J. Cook; William B. Butler; George W. Goetz; Darrin L. Johnson; Christopher J. Ruf; Barry F. Shaffer
Original assignee: TRW Vehicle Safety Systems Inc
Current assignee: ZF Passive Safety Systems US Inc
Priority date: 2006-06-13
Filing date: 2006-06-13
Publication date: 2007-12-20

Abstract

A method of filling containers (50) with gases (12) provides each container, when filled, with a first predetermined amount of a first gas and a second predetermined amount of a second gas. The method comprises the step of forming a mixture comprising first and second amounts of the first and second gases, respectively. The first and second amounts are greater than and are in proportion to the first and second predetermined amounts, respectively. The method further comprises the steps of: determining a sum of the first and second predetermined amounts; and adding a third amount of the mixture to each of the containers. The third amount is equal to the sum of the first and second predetermined amounts.

Description

TECHNICAL FIELD

The present invention relates to a method of filling containers with gases. More particularly, the present invention relates to a method of filling containers with predetermined amounts of first and second gases.

BACKGROUND OF THE INVENTION

It is known to provide an inflator for inflating an inflatable vehicle occupant protection device. One particular type of inflator is a heated gas inflator. In a heated gas inflator, a combustible mixture of gases is stored under pressure in a gas storage chamber. The heated gas inflator may include an outlet that is closed by a burst disk. An igniter assembly is associated with the gas storage chamber and is actuatable to ignite the combustible mixture of gases. When the combustible mixture of gases is ignited, the pressure of the gases within the gas storage chamber increases. The increased pressure ruptures the burst disk enabling the gases to exit the inflator through the outlet.
The combustible mixture of gases in a heated gas inflator generally includes hydrogen, an inert gas, and air. Actuation of the igniter assembly ignites the hydrogen to heat the inert gas and the air. Typically, the combustible mixture of gases has a precise amount of hydrogen. For example, the amount of hydrogen in the combustible mixture of gases may have a tolerance of approximately 0.001 grams. Additionally, since the molecular weight of hydrogen is low, the total mass of the hydrogen in the combustible mixture of gases may be less than one gram. When the total mass of the empty inflator is, for example, 1000 grams, adding less than one gram of hydrogen, with a tolerance of approximately 0.001 grams, tends to be difficult.
Currently, the process for adding the combustible mixture of gases to the inflator is time consuming and labor intensive. The process includes placing an empty inflator on a high precision scale and determining the mass of the empty inflator. The scale must be protected from air drafts, vibrations, and other variables that may alter the measured weight and thus, the determined mass, of the inflator. After the mass of the empty inflator is determined, hydrogen is introduced into the gas storage chamber of the inflator. After the hydrogen is added to the inflator and the scale has stabilized, the mass of the inflator and the stored hydrogen is determined. If the additional mass of the hydrogen is outside of the required tolerance, the amount of hydrogen in the gas storage chamber is adjusted and a subsequent determination of the mass of the inflator and the stored hydrogen is made.
When the amount of hydrogen added to the inflator is within its required tolerance, the inert gas is added to the gas storage chamber of the inflator. Generally, the combustible mixture of gases also has a precise amount of the inert gas. The inert gas is added to the gas storage chamber of the inflator using the same process as was used to add the hydrogen. After the precise amount of the inert gas has been added to the inflator, air is added to the gas storage chamber of the inflator to bring the pressure within the gas storage chamber to a predetermined level. When the pressure within the gas storage chamber reaches the predetermined level, the fill port for the gas storage chamber is sealed.

SUMMARY OF THE INVENTION

The present invention relates to a method of filling containers with gases. Each container, when filled, includes a first predetermined amount of a first gas and a second predetermined amount of a second gas. The method comprises the steps of: forming a mixture comprising first and second amounts of the first and second gases, respectively. The first and second amounts are greater than and are in proportion to the first and second predetermined amounts, respectively. The method also comprises the steps of: determining a sum of the first and second predetermined amounts; and adding a third amount of the mixture to each of the containers. The third amount is equal to the sum of the first and second predetermined amounts.
In accordance with another aspect, the present invention relates to a method of filling inflators with gases. Each inflator, when filled, includes a first predetermined amount of a first gas and a second predetermined amount of a second gas and is actuatable for inflating an inflatable safety device of a vehicle safety system. The method comprises the steps of: forming, in a mixing vessel, a mixture comprising first and second amounts of the first and second gases, respectively, wherein a ratio of the first amount to the second amount equals a ratio of the first predetermined amount of the first gas to the second predetermined amount of the second gas; determining a sum of the first and second predetermined amounts; and adding a third amount of the mixture to each of the inflators. The third amount is equal to the sum of the first and second predetermined amounts.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will become apparent to those skilled in the art to which the present invention relates upon reading the following description with reference to the accompanying drawings, in which:

FIG. 1 illustrates an inflator that has been filled with a combustible mixture of gases, in accordance with the method of the present invention;

FIG. 2 illustrates a vehicle safety system having the inflator of FIG. 1;

FIG. 3 schematically illustrates an apparatus for filling the inflator of FIG. 1; and

FIGS. 4A and 4B are schematic block diagrams illustrating a process of filling inflators, in accordance with the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an inflator 10 that has been filled with a combustible mixture of gases 12, in accordance with the method of the present invention. The inflator 10 illustrated is a heated gas inflator. The combustible mixture of gases 12 is stored under pressure in a gas storage chamber 14 of the inflator 10. Alternatively, the inflator 10 may be any type of inflator that includes a mixture of gases stored under pressure in a gas storage chamber 14.
FIG. 2 illustrates a vehicle safety system 18 having the inflator 10 of FIG. 1. The vehicle safety system 18 of FIG. 2 includes an inflatable safety device. The inflatable safety device of FIG. 2 is an inflatable curtain 20. The inflator 10, when actuated, provides inflation fluid for inflating the inflatable curtain 20. As an alternative to an inflatable curtain 20, the inflatable safety device may include an inflatable air bag, an inflatable seat belt, an inflatable knee bolster, an inflatable headliner, or a knee bolster operated by an inflatable air bag.
The inflatable curtain 20 of FIG. 2 is in a deflated condition and is stored within a housing 22 at a location adjacent both the side structure of a vehicle 26 and a roof of the vehicle. The side structure of the vehicle 26 includes an A-pillar 28, a B-pillar 30, a C-pillar 32, and side windows 34 and 36, respectively. FIG. 2 shows four brackets 40 securing the housing 22 and the inflatable curtain 20 to the side structure of the vehicle 26.
A conduit 44 connects the inflator 10 to the inflatable curtain 20. Upon actuation of the inflator 10, inflation fluid flows through the conduit 44 and into the inflatable curtain 20. In response to receiving the inflation fluid, the inflatable curtain 20 deploys from the deflated condition to an inflated condition to cover portions of the side structure of the vehicle 26, such as side windows 34 and 36.
As shown in FIG. 1, the inflator 10 includes a cylindrical, metal container 50. The container 50 includes a tubular body portion 52 having cylindrical inner and outer surfaces 54 and 56, respectively, and opposite first and second ends 58 and 60, respectively. An igniter end cap 66 closes the first end 58 of the tubular body portion 52. The igniter end cap 66 includes an annular flange portion 68 that is fixed to the tubular body portion 52 and an igniter support portion 70 that supports an actuatable igniter 74. The igniter support portion 70 of the igniter end cap 66 includes a passage 76 through which combustion products produced by actuation of the igniter 74 may pass. Prior to actuation of the igniter 74, a rupturable burst disk 78 closes the passage 76.
A diffuser end cap 84 closes the second end 60 of the tubular body portion 52. The diffuser end cap 84 includes a tubular end portion 86 having inner and outer surfaces 88 and 90, respectively. A circular gas fill port 92 extends through the tubular end portion 86 of the diffuser end cap 84. The diffuser end cap 84 also includes an end portion 96 that includes an annular end wall portion 100 and a tubular discharge portion 102. The tubular discharge portion 102 of the end portion 96 extends axially away from the annular end wall portion 100 in a direction parallel to an axis A. The tubular discharge portion 102 includes a passage 106 that provides an exit path for inflation fluid to flow out of the container 50.
Prior to actuation of the igniter 74, a rupturable burst disk 110 closes the passage 106 of the tubular discharge portion 102 of the diffuser end cap 84. The burst disk 110 is designed to rupture when subjected to a predetermined pressure differential.
The tubular body portion 52, the igniter end cap 66, and the diffuser end cap 84 collectively define the gas storage chamber 14. The gas storage chamber 14 extends along axis A between the igniter end cap 66 and the diffuser end cap 84. The inner surface 54 of the tubular body portion 52 and the inner surface 88 of the tubular end portion 86 of the diffuser end cap 84 define a radial outer boundary of the gas storage chamber 14.
When the igniter 74 of the inflator 10 receives an actuation signal from electronic circuitry 114 (FIG. 2) of the vehicle safety system 18, the igniter 74 is actuated. Combustion products from actuation of the igniter 74 travel through the passage 76 in the igniter end cap 66, rupture the burst disk 78, and enter the gas storage chamber 14. The combustion products heat and ignite the combustible mixture of gases 12 that is stored under pressure within the gas storage chamber 14. The heating and ignition of the combustible mixture of gases 12 increases the pressure within the gas storage chamber 14. When the predetermined pressure differential across the burst disk 110 is reached, the burst disk 110 is ruptured. Inflation fluid resulting from heating and igniting the combustible mixture of gases 12 exits the inflator 10 through the passage 106 of the tubular discharge portion 102 of the diffuser end cap 84.
FIG. 3 schematically illustrates an apparatus 120 for filling the inflator 10 with a combustible mixture of gases. As an example, the apparatus 120 of FIG. 3 will be described as filling the inflator 10 with a combustible mixture of gases that includes hydrogen, argon, and air. The apparatus 120 of FIG. 3 illustrates three vessels 122, 124, and 126. Vessel 122 contains a stored quantity of hydrogen gas, under pressure. Vessel 124 contains a stored quantity of argon, under pressure. Vessel 126 contains a stored quantity of air, under pressure.
The apparatus 120 also includes a mixing vessel 130. The mixing vessel 130 has a volume that is significantly greater than the volume of the gas storage chamber 14 of the inflator 10. In a preferred embodiment of the invention, the volume of the mixing vessel 130 is over one thousand times greater than the volume of the gas storage chamber 14 of the inflator 10.
A conduit 134 connects vessel 122 to the mixing vessel 130. A valve 136 attaches the conduit 134 to the mixing vessel 130. When the valve 136 is open, hydrogen flows into the mixing vessel 130. A conduit 140 connects vessel 124 to the mixing vessel 130. A valve 142 attaches the conduit 140 to mixing vessel 130. When the valve 142 is open, argon flows into the mixing vessel 130.
FIG. 3 illustrates a scale 146 that is associated with the mixing vessel 130. The scale 146 is used for monitoring the amounts of hydrogen and argon in the mixing vessel 130. The amounts of hydrogen and argon that are mixed together in the mixing vessel 130 are proportional to predetermined amounts of hydrogen and argon in the combustible mixture of gases 12 contained in the inflator 10. For example, assume that a ratio of the predetermined amount, by mass, of hydrogen in the combustible mixture of gases 12 to the predetermined amount, by mass, of argon in the combustible mixture of gases 12 is 1/33. The ratio of the amount, by mass, of hydrogen and the amount, by mass, of argon that are mixed together in the mixing vessel 130 is also 1/33. The amounts of hydrogen and argon mixed together in the mixing vessel 130, however, are significantly greater than the predetermined amounts used to fill one inflator 10. In a preferred embodiment, the mixing vessel 130 holds enough hydrogen and argon to fill over one thousand inflators.
To ensure a proper mixture of the hydrogen and argon in the mixing vessel 130, the scale 146 is used to determine the mass of the empty mixing vessel 130. The valve 136 is then opened and a quantity of hydrogen flows into the mixing vessel 130. The valve 136 is closed and the scale 146 is used to determine mass of the hydrogen that was added to the mixing vessel 130. Since the amount of hydrogen added to the mixing vessel 130 is preferably enough to fill over one thousand inflators, the added hydrogen will have a sufficient mass so as to be easily monitored using the scale.
After the amount of hydrogen that was added to the mixing vessel 130 is determined, the amount of argon to be added to the mixing vessel 130 is calculated. The amount of argon to be added to the mixing vessel 130 is determined from the ratio of the predetermined amount of hydrogen to the predetermined amount of argon in the combustible mixture of gases 12 and from the determined amount of hydrogen so that mass ratio of hydrogen to argon in the mixing vessel 130 is equal to the mass ratio of hydrogen to argon to be added to the inflator, e.g., a mass ratio of 1/33.
With reference again to FIG. 3, the apparatus 120 also includes a member 150 for temporarily attaching to the inflator 10. The member 150 includes first and second input lines 152 and 154, respectively, and a single output line 156. A first valve 160 is associated with the first input line 152. A second valve 162 is associated with the second input line 154.
A conduit 166 connects the mixing vessel 130 to the first valve 160. When the first valve 160 is open, a mixture of hydrogen and argon flows into the first input line 152 of the member 150 and is directed into the gas storage chamber 14 of the inflator 10. As a result, when the first valve 160 is open, hydrogen and argon are added simultaneously to the gas storage chamber 14 of the inflator 10.
A conduit 168 connects the vessel 126 to the second valve 162. When the second valve 162 is open, air flows into the second input line 154 of the member 150 and is directed into the gas storage chamber 14 of the inflator 10.
To fill the inflator 10 with the combustible mixture of gases 12, the member 150 is secured to the inflator 10 so that the output line 156 of the member directs a flow of gas through the fill port 92 (FIG. 1) and into the gas storage chamber 14 of the inflator 10.
Next, the sum of the predetermined amounts of hydrogen and argon is determined. For purposes of example, assume that the inflator 10 is a 180 cm³inflator that holds approximately 75 grams of the combustible mixture of gases 12. Also, for purposes of example, assume that the combustible mixture of gases 12 includes 12% by volume hydrogen, 20% by volume argon, and 68% by volume air. When filled with the combustible mixture of gases 12, the inflator 10 will hold approximately 0.65 grams of hydrogen, 21.47 grams of argon, and 52.88 grams of air at a pressure of 6000 p.s.i. to 7000 p.s.i.
As set forth in the Background of the Invention, adding such a small mass of hydrogen to the inflator, with a tolerance of approximately 0.001 grams, tends to be difficult. Instead of adding the approximately 0.65 grams of hydrogen to the inflator 10 and then later adding the approximately 21.47 grams of argon, the hydrogen and argon are simultaneously added to the inflator 10 according the method of the present invention.
In our example, the determined sum of the predetermined amounts of hydrogen and argon equals approximately 22.12 grams (the sum of 0.65 grams and 21.47 grams). After the sum of the predetermined amounts is determined, an amount of the mixture of hydrogen and argon equal to the sum of the predetermined amounts, e.g., 22.12 grams, is added to the gas storage chamber 14 of the inflator 10. A scale 174 is used for determining the amount (mass) of the mixture of hydrogen and argon that has been added to the inflator 10.
Since both the hydrogen and the argon have associated tolerances, assuming the proportion of the hydrogen and argon in the mixture is proper (e.g., a ratio of 1/33) and assuming that the mixture of hydrogen and argon flowing into the inflator 10 is homogenous, the tolerance for the mixture of hydrogen and argon will be larger than the individual tolerances for the hydrogen and the argon. For example, if the tolerance for the hydrogen is 0.001 grams and the tolerance for the argon is 0.005 grams, the tolerance for the mixture of hydrogen and argon may be greater than 0.005 grams while still maintaining the proper amounts of hydrogen and argon in the inflator 10. This results from the fact that the hydrogen only accounts for approximately 1/34 (0.65 grams H₂/22.12 grams mixture) of the total added mass of the mixture and the argon only accounts for 33/34 (21.47 grams Ar/22.12 grams mixture) of the total added mass. Thus, when the amount of the mixture of hydrogen and argon added to the inflator 10 is within a 0.005 gram tolerance, the amount of hydrogen added is within its 0.001 gram tolerance (0.005 grams times 1/34 equals 0.000147 grams) and the amount of argon added is also within its 0.005 gram tolerance (0.005 grams times 33/34 equals 0.000485 grams).
After the mixture of hydrogen and argon is added to the gas storage chamber 14 of the inflator 10, the second valve 162 is opened and air is added to the gas storage chamber 14 of the inflator 10. the scale 174 is used to determine the weight of the air added to the storage chamber 14 of the inflator 10. After the air is added to the inflator, the fill port 92 of the inflator 10 is closed and the inflator is removed from the apparatus 10. FIG. 1 illustrates a closure member 180 closing the fill port 92 of the inflator 10.
FIGS. 4A and 4B are schematic block diagrams illustrating a process 400 of filling inflators. For purposes of example, the discussion of FIGS. 4A and 4B will refer to the example given above, i.e., an inflator holding 75 grams of a combustible mixture of gases of which approximately 0.65 grams is hydrogen, approximately 21.47 grams is argon, and approximately 52.88 grams is air.
As shown in FIG. 4A, the process 400 begins at step 402. At step 404, a first gas, e.g., hydrogen, is added to the mixing vessel 130. At step 406, the amount of the first gas added to the mixing vessel 130 is determined. To determine the amount of the first gas added to the mixing vessel 130, the mass of the mixing vessel 130, when empty, is determined prior to the first gas being added. The mass of the mixing vessel 130 is then determined after the addition of the first gas. The difference between the two determined masses represents the mass of the first gas added to the mixing vessel. Step 406 does not require any precise amount of the first gas to be added to the mixing vessel 130 as long as the amount of first gas added is greater than a predetermined amount for filling one inflator. As set forth above, the amount of the first gas added to the mixing vessel 130 is preferably enough to fill a large number of inflators, such as one thousand inflators. For purposes of example, assume that 700 grams of hydrogen was added to the mixing vessel 130 at step 406.
At step 408, the amount of the second gas, e.g., argon, to be added to the mixing vessel 130 is calculated. The mass ratio of the first and second gases in the mixing vessel 130 should be equal to the mass ratio of the predetermined amounts of the first and second gases in the inflator. In our example, the mass ratio of hydrogen to argon is 1/33. Thus, the amount of argon to be added to the mixing vessel 130 at step 408 equals thirty-three times the amount of hydrogen added at step 406. In our example, 700 grams of hydrogen was added to the mixing vessel 130 at step 406. Therefore, at step 408, the calculated amount of the argon is 23.1 kilograms.
At step 410, the calculated amount of the second gas is added to the mixing vessel 130. At step 412, the amount of the second gas added to the mixing vessel 130 is determined. To determine the amount of the second gas added to the mixing vessel 130, the mass of the mixing vessel 130 after the addition of the second gas is determined. The previously determined mass of the mixing vessel 130 after the addition of the first gas and prior to the addition of the second gas is subtracted from the determined mass of the mixing vessel 130 after the addition of the second gas. The difference between the two determined masses represents the mass of the second gas added to the mixing vessel 130.
At step 414, a determination is made as to whether the correct amount of the second gas has been added to the mixing vessel 130. The determination at step 414 is made by comparing the determined amount of the second gas added to the mixing vessel 130 from step 412 to the calculated amount of the second gas from step 408. When the determined amount of the second gas added is within a predetermined tolerance of the calculated amount of the second gas, the determination at step 414 is affirmative.
In response to a negative determination at step 414, the process 400 proceeds to step 416 and the amount of the second gas in the mixing vessel 130 is increased if the amount of the second gas is too low. The amount of the second gas can not become too high, because the systems (in a manner not shown), is constantly being monitored by continually weighing the second gas in the mixing vessel and closing off the flow of the second gas when the correct weight is in the mixing vessel 130. From step 416, the process 400 returns to step 414. In response to an affirmative determination at step 414, the process proceeds to step 418.
At step 418, the sum of the predetermined amounts of the first and second gas to be added to an inflator is determined. In our example, the predetermined amount of the first gas, hydrogen, is 0.65 grams and the predetermined amount of the second gas, argon, is 21.47 grams. Therefore, the sum of the predetermined amounts that is determined at step 418 is 22.12 grams grams.
As shown with reference to FIG. 4B, the process 400 proceeds from step 418 to step 420. At step 420, an empty inflator is inserted into the apparatus 120. When the empty inflator is inserted into the apparatus 120, the member 150 of the apparatus 120 for directing gases into the inflator is connected to the inflator so as to direct gases through the fill port of the inflator and into the gas storage chamber. At step 422, a mass of the empty inflator is determined.
At step 424, the mixture of the first and second gases is added to the inflator. The amount of the mixture added to the inflator is the amount determined at step 418. At step 426, the amount of the mixture of the first and second gases added to the inflator is determined. To determine the amount of the mixture added to the inflator, the mass of the inflator after the addition of the mixture of gases is determined. The previously determined mass of the empty inflator is subtracted from the determined mass of the inflator after the addition of the mixture of gases. The difference between the two determined masses represents the mass of the mixture of gases added to the inflator.
At step 428, a determination is made as to whether the correct amount of the mixture of gases has been added to the inflator. The determination at step 428 is made by comparing the determined amount of the mixture of gases added to the inflator from step 426 to the determined sum from step 418. When the determined amount of the mixture of gases added is within a predetermined tolerance of the determined sum, the determination at step 428 is affirmative.
In response to a negative determination at step 428, the process 400 proceeds to step 430, and the amount of the mixture of gases in the inflator is adjusted by either adding or removing an amount of the mixture. From step 430, the process 400 returns to step 428. In response to an affirmative determination at step 428, the process 400 proceeds to step 432. At step 432, a predetermined amount of air is added to the inflator. As noted above the air added to the inflator is weighted. The air increases the pressure of the gases in the gas storage chamber of the inflator to a predetermined pressure. At step 434, the fill port of the inflator is closed and sealed and, at step 436, the inflator is removed from the apparatus.
From step 436, the process 400 proceeds to step 438. At step 438, the amount of the mixture of the first and second gases remaining in the mixing vessel 130 is determined. The amount of the mixture remaining may be determined by monitoring the total mass of the mixing vessel 130 and the mixture of gases. At step 440, a determination is made as to whether the remaining amount of the mixture of gases is greater than the sum of the predetermined amounts from step 418. When the determination at step 440 is affirmative, and the amount of the mixture of gases remaining in the mixing vessel 130 is greater than the sum of the predetermined amounts from step 418, the process 400 proceeds to step 442 and another empty inflator is inserted into the apparatus 120 to be filled. From step 442, the process 400 returns to step 422. When the determination at step 440 is negative, the process 400 proceeds to step 444 and ends.
From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications. For example, nitrogen may be used in the process as a substitute for argon. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.

Claims

1. A method of filling containers with gases, each container, when filled, including a first predetermined amount of a first gas and a second predetermined amount of a second gas, the method comprising the steps of:

forming a mixture comprising first and second amounts of the first and second gases, respectively, the first and second amounts being greater than and in proportion to the first and second predetermined amounts, respectively;

determining a sum of the first and second predetermined amounts; and

adding a third amount of the mixture to each of the containers, the third amount being equal to the sum of the first and second predetermined amounts.

2. The method of claim 1 wherein the step of forming a mixture further includes the steps of:

determining a ratio of the first predetermined amount to the second predetermined amount;

adding the first amount of the first gas to a mixing vessel;

determining the second amount of the second gas to be added to the mixing vessel so that the ratio of the first amount to the second amount equals the determined ratio of the first predetermined amount to the second predetermined amount; and

adding the determined second amount of the second gas to the mixing vessel.

3. The method of claim 1 wherein the step of adding a third amount of the mixture to each of the containers further includes the steps of:

adding mixture to a first container;

determining the amount of mixture added to the first container;

comparing the determined amount of mixture added to the third amount; and

adjusting the amount of mixture added when the determined amount of mixture added is outside of a predetermined tolerance relative to the third amount.

4. The method of claim 3 wherein the step of determining the amount of mixture added to the first container includes the steps of:

determining a mass of the first container when empty;

determining a mass of the first container after the mixture has been added; and

subtracting the determined mass of the first container when empty from the determined mass of the first container after the mixture has been added.

5. The method of claim 3 further including the steps of:

replacing the first container with a second container when the determined amount of mixture added to the first container is within the predetermined tolerance;

adding mixture to the second container;

determining the amount of mixture added to the second container;

comparing the determined amount of mixture added to the second container to the third amount; and

adjusting the amount of mixture added to the second container when the determined amount of mixture added is outside of the predetermined tolerance relative to the third amount.

6. The method of claim 5 further including the step of determining, prior to replacing the first container with the second container, whether an amount of mixture remaining is greater than the sum of the first and second predetermined amounts.

7. The method of claim 1 further including the step of adding a third gas to each of the containers after the third amount of the mixture has been added.

8. The method of claim 7 wherein the step of adding a third gas to each of the containers includes the step of increasing a pressure of the gases in gas storage chambers of each of the containers to a predetermined pressure.

9. The method of claim 7 further including the step of closing a fill port of each of the containers after the third gas has been added.

10. A method of filling inflators with gases, each inflator, when filled, including a first predetermined amount of a first gas and a second predetermined amount of a second gas and being actuatable for inflating an inflatable safety device of a vehicle safety system, the method comprising the steps of:

forming, in a mixing vessel, a mixture comprising first and second amounts of the first and second gases, respectively, wherein a ratio of the first amount to the second amount equals a ratio of the first predetermined amount of the first gas to the second predetermined amount of the second gas;

determining a sum of the first and second predetermined amounts; and

adding a third amount of the mixture to each of the inflators, the third amount being equal to the sum of the first and second predetermined amounts.