CHEMISTRY BEHIND AIRBAGS
A Term Paper presented to:
LEIZEL FLORENDO TANGONAN
Of the requirement
BIA DANESSA N. FERRER
BEA PAULA ARZAGA
BACHELOR OF SCIENCE IN PETROLEUM ENGINEERING
PALAWAN STATE UNIVERSITY
TABLE OF CONTENTS
- LITERATURE REVIEW————————————————————–3-4
ARZAGA, BEA PAULA.,FERRER, BIA DANESSA N., “Chemistry Behind Airbags”, Palawan State University, October 2014.
Instructor: Ms. Liezl Florendo Tangonan
The purpose of this paper is to study about the chemistry behind airbags, giving you some knowledge about how airbags work and about their effectiveness in preventing serious injury or death. It will also answer these questions: a.)How the presence of an airbag actually protects you? b.)How do airbags operate or work? c.)What are the limitations and capabilities of ensuring the safety of car owners and passengers? d.)How do airbags save lives? e.)What about the Gas Used to Fill the Airbag? f.)How is it related to gas laws?
This has been done by our joint research using the internet, collecting data from different sources etc., summing them up, assessing, evaluating and making a concrete conclusion.
The anticipated outcome of this paper is to have a better public understanding of how airbags work /operates, for the car owners to be aware of the use and importance of airbags, to encourage them to exert their effort to provide, upgrade or equipped their cars with airbags and to remind them of the importance of guarantying our safety. In addition, it is hoped that everyone will be alerted to the environmental considerations concerning airbags.
Background of the Study
As we can observe today and also based on statistics, Philippines is one of those Country who have a great number of cars and car owners. According to Philippine National Statistical Coordination Board the Car Registrations in Philippines as of December 2013 is 103576.
It’s not that really surprising, it is very noticeable. As a matter of fact, heavy traffic is one of the everyday scenarios for most of the part of the country especially in the cities, aside from that, we can observed even just in the campus- Palawan State University, along the parking lots are lined numbers of cars of different sorts owned by the school faculties and staffs as well as students, and also those everyday cars entering the premises sending their children to and fro.
And inclined to this, of course is the increasing numbers of vehicular accidents specially car accidents.
And mentioning about cars, Chemistry is not usually associated with cars, but there’s one very important piece of safety equipment which relies on a cleverly devised chemical reaction. And it’s one that most drivers would rather not experience first-hand – air bags.
Every car boasts of having an airbag. They are very simple but also amazingly clever and they have saved many lives since their introduction in early 1980s. But do you know what an airbag is and how and why is it considered as an asset to your vehicle? Have you ever wondered from where does this amount of gas comes in such short interval of time? Where is this gas stored? What makes airbag to inflate? Do the money spend on it really worth?
We will tell you why…
Most modern cars are equipped with an airbag. Just like we said earlier, they are safety devices, just like seat belts. They are cushions that are built and designed inside every car to inflate rapidly during an automobile collision and provide protection to you and your near and dear ones when strike by interior objects such as the steering wheel or a window during mishaps or accidents while driving the car. They inflate and then immediately deflate as you impact it. It is considered as one of the most important safety innovations of recent decades. These devices have slashed the highway death toll.
So, our main concern here is the safety of course, we chose this because we would like to know how airbags work, how is it related with gas laws, why is it a must or why should car owners equipped their cars with airbags, we would like to know if we can really guarantee our safety, our lives and our money as well for spending for the cost.
REVIEW OF RELATED LITERATURE
Because of the increasing number of cars, the number of car accident also increases, and one of the reason for this is the condition of the car and it is the responsibility of Drivers and car owners to check and provide their cars a regular check up and upgrade, and this is to ensure the safety of their passengers as well as the driver or owner himself. Many car owners are aware but not really exerting their efforts on upgrading their cars with safety device such as airbags. Airbags today are considered as one of the most important safety innovations.
Airbag is defined by the wiktionary.org as a protective system in automobiles in which when a crash occurs, bag containing nitrogen, formed by the explosive decomposition of sodium azide, quickly inflates in front of the driver or passenger, preventing injury to the head. Side air bags, including the back seat passengers, also prevent injury.
In recent years, increased reports in the media concerning deaths or serious injuries due to airbag deployment have led to a national discussion about the usefulness and “safety” of airbags. Questions are being raised as to whether airbags should be mandatory, and whether their safety can be improved. Questions such as: How much does the number of deaths or serious injuries decrease when an airbag and seat belt are used, as compared to when a seat belt is used alone? How many people are airbags killings or seriously injuring? Do the benefits of airbags outnumber the disadvantages? How can airbags be improved?
It was stated form topspeedracer.com , that Twenty years ago, when vehicle airbag systems were first being offered, many people joked about how airbags worked. Some likened them to stove-top popcorn, of the type that started out looking like a pie pan and ended up looking like a lumpy silver balloon, while others thought they were just really big balloons. Either way, most people thought and many people still think that once an airbag deploys, it remains inflated leaving you cheek to cheek with talcum coated nylon until help arrives.
According to the Insurance Institute for Highway Safety, cars with passenger airbags, along with side impact airbag, reduce significantly the number of deaths due to auto accidents. That is a significant factor when considering the importance of having passenger car airbags. Even with the protection a seatbelt and vehicle restraint system provides in the event of a crash, the chance of surviving a serious crash with airbags increase significantly. In addition, according to the statistics, airbags have saved lives and have lowered the number of severe injuries. These statistics are continuing to improve, as airbags become more widely used. Nevertheless, as the recent reports have shown, there is still a need for development of better airbags that do not cause injuries. Also, better public understanding of how airbags work will help people to make informed and potentially life-saving decisions about using airbags.
Another information about airbags is provided by the study conducted by National Geographic,Airbags- the idea of using a giant balloon to cushion you if you crash, has been around since the 1950’s. Yet, it wasn’t until 1974 that General Motors offered the first commercial car, with a driver side air bag. Your driver airbag works in a very similar way to a rocket. They both use solid fuel. In your car this is found in the compartment behind the steering wheel. Like this. When it’s ignited it’s contained and the gases released inflate the airbag. Whereas with a rocket, the solid fuel is at the bottom. So when you ignite it, the uncontained release of energy propels the rocket skyward. The gas blows up the airbag pretty quickly. The airbag’s inflated in roughly 35 mili seconds. Which to scale it for you, It takes you approximately 200 mili seconds to blink. You don’t need to worry about suddenly being hit by an airbag, because a sensor in your car continually measures acceleration and deceleration. It will only deploy the airbag when it senses a dramatic deceleration resulting from a sudden impact. And the bags themselves are getting clever. They can now alter the amount they inflate according to the weight and position of the person. Which means they’re less likely to give you a hard punch in the face. In today’s cars airbags can be in the roof, in the side, in your seat. There are even airbags to put you in the right position before you hit another airbag. But wherever they are, an airbag will always react so quickly that if you blink, you’ll miss it.
The air bag system can be broken down into two main components. These are the impact sensor and the air bag module unit. The impact sensor does what its name implies, senses impacts. The sensors are set to a sensitivity level where they will only deploy in an accident that is equal to or greater than a 12 mph crash into a concrete wall. The sensors function by detecting automobile deceleration. When the automobile decelerates at a rapid rate, the sensors are tripped. This deceleration detecting is the job of two or more deceleration sensors, placed at the front of the car. When the sensors go off, they send an electrical current to the air bag module unit, causing it to deploy. The air bag module unit consists of an inflator assembly, a nylon bag, and a breakaway cover. This unit is typically located in the steering wheel column on the driver’s side or in the dashboard on the passenger’s side. The electrical current from the sensors travels to the inflator assembly, where it causes a tiny initiator to be fired. This initiator creates a spark which ignites a propellant, which in most air bags is sodium azide. The reaction creates nitrogen gas. Cinders are removed and the gas is cooled through a filtration screen also inside the assembly. The nitrogen gas is what causes the air bag to inflate. This inflation occurs in an average of only 30 milliseconds. When an occupant plunges into the air bag, the gas if forced backwards through vents, a process which takes another forty-five milliseconds. The whole sequence from initial detection of a crash, until the air bag is fully deployed, happens very quickly. This quickness is required in order to protect those inside of the car, and was one of the major obstacles that needed to be overcome in the development of the air bag. (http://web.bryant.edu/)
RESEARCH METHODS AND PROCEDURES
- The researchers chose the topic “Chemistry behind Airbags” because of the subject’s relevance to gas laws. This certain topic is relevant to gas laws by its chemical content; gas component-NaN3 , KNO3 and SiO2 .
- The researchers hypothetically thought of the possibilities of hazard caused by the airbags itself, the gas used to make the airbag functional, the mechanism used to fully utilize the airbags, and the air bags’ relation to gas laws.
- The researchers came up with following questions for this particular study entitled “Chemistry behind Airbags” to know more about this topic: 1) Is the passenger airbag truly safe?; 2) What about the gas used to fill the airbag?; 3) What prompts the airbag to inflate by way of its reaction?; and 4) How is it related with gas laws?
- The researchers gathered/collected data through online references (see bibliography on page __ for reference). By generally searching for facts, they reviewed each worthy websites and chose the finest data to create an accurate and reliable information.
- The researchers’ gathered data were all contrasted and compared. Through that process, the data were criticized to identify differences and prove facts.
- The researchers’ collection of data were thoroughly calculated and analyzed to ensure accuracy. Extensive research was made to support facts and confirm anomalies.
- The researchers premeditated the collection of data as well as the results in hand cautiously. The premeditation furnished the summarization of the information from the collected data and results.
- The researchers carefully assessed and evaluated each necessary data in hand to produce precise and consistent information. The product then is well utilized in serving its purpose, to provide further knowledge to the researchers on the subject matter, to the study.
- The researchers were able to provide their queries with corresponding answers from the data they processed which became the information they had. That information gave the elements to the answers they sought.
- From the corresponding answers they had for their questions, the researchers drew their conclusion on “Chemistry behind Airbags”. Those answers provided them all the necessary information to produce a conclusion for their study.
Air bags are used to protect a driver and a passenger from a crash. An airbag is made up of three parts. The first part is the bag itself that is made out of think nylon fabric and is folded in the steering wheel or the dashboard of your car. The second part of the airbag is the sensor that informs the bag to inflate when the car meets with an accident. The sensor detects the collision force and calculates the force equal to running into a brick wall at around 10 to 15 miles per hour. The third part consists of an inflation system.
An airbag fills up with a mixture of potassium and sodium azide which creates nitrogen.
When any collision takes place, the sensor detects the collision force and informs the bag to inflate. At that time, the sodium azide and potassium nitrate react quickly and produces a large pulse of hot nitrogen gas. The gas inflates the bag in turn and the bag literally bursts out of the steering wheel or the dashboard. After a second, the bag starts deflating with the help of the holes present on it to get out of your way.It is activated when the requisite threshold is reached.
There are two types of airbags used in the cars; frontal and various types of side-impact airbags. Advanced frontal airbags determine if and with what level of power the driver airbag and the passenger airbag will inflate. Side impact airbags or SABs are devices that will help protect your chest and head in case of any crash involving the side of the vehicle.
Cornstarch or talcum powder is generally used within the storage system for airbags to keep everything flexible and stick-proof. It also helps to ensure that the airbag will deploy properly.
An overview of how does airbag work
- When a car hits something, it starts to decelerate (lose speed) very rapidly.
- An accelerometer (electronic chip that measures acceleration or force) detects the change of speed.
- If the deceleration is great enough, the accelerometer triggers the airbag circuit. Normal braking doesn’t generate enough force to do this.
- The airbag circuit passes an electric current through a heating element (a bit like one of the wires in a toaster).
- The heating element ignites a chemical explosive. Older airbags used sodium azide as their explosive; newer ones use different chemicals.
- As the explosive burns, it generates a massive amount of harmless gas (typically either nitrogen or argon) that floods into a nylon bag packed behind the steering wheel.
- As the bag expands, it blows the plastic cover off the steering wheel and inflates in front of the driver. The bag is coated with a chalky substance such as talcum powder to help it unwrap smoothly.
- The driver (moving forward because of the impact) pushes against the bag. This makes the bag deflate as the gas it contains escapes through small holes around its edges. By the time the car stops, the bag should have completely deflated.
Is the Passenger Airbag Truly Safe?
To help address issues with airbag safety, aside from recommending the use of seat belts, auto makers are also looking at how to be proactive in helping passengers benefit from passenger side airbags instead of being harmed by them.
Automobile airbags have been a critical advance in driver and passenger safety, but they can cause injury or even death if not used properly.
Still, statistics show that passenger airbags have saved many more lives than they have harmed. While passenger airbags may be linked to some injury or death, chances are you will be safer using them, rather than not.
What about the Gas Used to Fill the Airbag?
Although we don’t usually associate automobiles with chemistry, a lot of chemistry takes place in a working car–the burning of gasoline to run the engine, for example, and chemical reactions in the battery to generate electricity. Another reaction–one that most drivers would just as soon not experience firsthand–involves the air bag. Air bags are not inflated from some compressed gas source but rather from the products of a chemical reaction. The chemical at the heart of the air bag reaction is called sodium azide, or NaN3.
Under normal circumstances, this molecule is quite stable. If heated, though, it will fall apart. The chemical equation 2 NaN3 –> 2 Na + 3 N2 describes exactly how it falls apart. Notice that the second product of the above reaction is N2, also known as nitrogen gas. A handful (130 grams) of sodium azide will produce 67 liters of nitrogen gas–which is enough to inflate a normal air bag.
That’s not the only chemistry involved. Notice that the other chemical into which sodium azide falls apart is Na, or sodium. Sodium is a very reactive metal that will react rapidly with water to form sodium hydroxide; as a result, it would be quite harmful if it got into your eyes, nose or mouth. So to minimize the danger of exposure, air bag manufacturers mix the sodium azide with other chemicals that will react with the sodium and, in turn, make less toxic compounds.
Chemical Reactions Used to Generate the Gas
(1) 2 NaN3 → 3 N2 + 2 Na
(2) 10 Na + 2 KNO3 → N2 + K2O + 5 Na2O
(3) K2O + 2 SiO2 + Na2O → K2O3Si + Na2O3Si (silicate glass)
Most car-manufactures prefer KNO3 and not NaNO3, as it’s less hygroscopic. To ensure the air bag is fully operational even in the presence of moisture, it’s essential to choose non-hygroscopic components, otherwise the reaction may fail.
What prompts an air bag to inflate by way of this reaction?
There are sensors in the front of the automobile that detect a collision. These sensors send an electric signal to the canister that contains the sodium azide and the electric signal detonates a small amount of an igniter compound. The heat from this ignition starts the decomposition of the sodium azide and the generation of nitrogen gas to fill the air bag. What is particularly amazing is that from the time the sensor detects the collision to the time the air bag is fully inflated is only 30 milliseconds, or 0.03 second. Some 50 milliseconds after an accident, the car’s occupant hits the air bag and its deflation absorbs the forward-moving energy of the occupant.
The Macroscopic Picture of Gas Behavior: Ideal-Gas Laws
Calculation of the Amount of Gas Needed
Nitrogen is an inert gas whose behavior can be approximated as an ideal gas at the temperature and pressure of the inflating airbag. Thus, the ideal-gas law provides a good approximation of the relationship between the pressure and volume of the airbag, and the amount of N2 it contains. (The ideal-gas law is PV = nRT,where P is the pressure in atmospheres, V is the volume in liters, n is the number of moles, R is the gas constant in L·atm/mol·K (R = 0.08205 L·atm/mol·K), and T is the temperature in Kelvin.) A certain pressure is required to fill the airbag within milliseconds. Once this pressure has been determined, the ideal-gas law can be used to calculate the amount of N2 that must be generated to fill the airbag to this pressure. The amount of NaN3 in the gas generator is then carefully chosen to generate this exact amount of N2 gas.
Estimating the Pressure Required to Fill the Airbag
An estimate for the pressure required to fill the airbag in milliseconds can be obtained by simple mechanical analysis. Assume the front face of the airbag begins at rest (i.e., initial velocity vi = 0.00 m/s), is traveling at 2.00×102 miles per hour by the end of the inflation (i.e., final velocity vf = 89.4 m/s), and has traveled 30.0 cm (the approximate thickness of a fully-inflated airbag).
following formula encountered in any basic physics text:
vf2 – vi2 = 2ad.
The force exerted on an object is equal to the mass of the object times its acceleration (F = ma) ; therefore, we can find the force with which the gas molecules push a 2.50-kg airbag forward to inflate it so rapidly. 2.5 kg is a fairly heavy bag, but if you consider how much force the bag has to withstand, it becomes apparent that a lightweight-fabric bag would not be strong enough. Note: In the calculation below, we are assuming that the airbag is supported in the back (i.e., all the expansion is forward), and that the mass of the airbag is all contained in the front face of the airbag.
F = ma
Pressure is defined as the force exerted by a gas per unit area (A) on the walls of the container (P = F/A), so the pressure (in Pascals) in the airbag immediately after inflation can easily be determined using the force calculated above and the area of the front face of the airbag (the part of the airbag that is pushed forward by this force). Note: The pressure calculated is gauge pressure.
The amount of gas needed to fill the airbag at this pressure is then computed by the ideal-gas law (see Questions below). Note: the pressure used in the ideal gas equation is absolute pressure. Gauge pressure + atmospheric pressure = absolute pressure.
Deflation of the Airbag
When N2 generation stops, gas molecules escape the bag through vents. The pressure inside the bag decreases and the bag deflates slightly to create a soft cushion. By 2 seconds after the initial impact, the pressure inside the bag has reached atmospheric pressure.
Newer, more advanced airbags offer even more benefits than their predecessors. Airbags inflate at incredibly high speeds, meaning that it is a common occurrence for an airbag to break a nose or give a black eye. In the case of smaller occupants, the risk of injury from the airbag, itself, increases. New advances have created airbags that inflate with less force and are activated during lower-speed crashes, meaning that the airbag causes less damage and jumps into action in more non-lethal, yet damaging crashes.
When purchasing a car, make sure to check out the airbags and their features. While almost all new cars have airbags installed, they vary as to how many, where they are placed, and how well they perform. Check out safety ratings and when given the option, a safer car is the best, most invaluable, choice.
The main advantage of having car airbags for your passengers is that they provide an additional level of protection in the event of a car accident. This added protection can be the difference in some circumstances between life and death.
In most cars today you will find an airbag. The airbag has three main parts. First the bag, which is made of a thin nylon fabric, holds the chemicals and sensors and folds into the steering wheel or the dashboard. The electronic components contain a sensor that detects a collision force equal to running into a brick wall at about 10-15 mph and an igniter that detonates the first chemical reaction. The third component contains NaN3, KNO3 and SiO2.
How the airbags operate which include the gases and chemical reactions involved in inflation and deflation is associated with chemistry. Air bags are not inflated from some compressed gas source but rather from the products of a chemical reaction. And the chemical at the heart of the air bag reaction is called sodium azide, or NaN3. The chemicals involved in airbag deployment are NaN3, Na, K2O, SiO2, KNO3 and the three chemical reactions involved are the following: (1) 2 NaN3 → 3 N2 + 2 Na-(2) 10 Na + 2 KNO3 → N2 + K2O + 5 Na2O-This reaction produces even more nitrogen gas, and fuses the oxides into a glass-like matrix. This reaction also produces a lot of heat, causing the bag to inflate even faster (3) K2O + 2 SiO2 + Na2O → K2O3Si + Na2O3Si (silicate glass). Using the ideal gas equation, 0.3 g of N2 gas are generated when the airbag deploys and 0.6 moles of NaN3 are needed in order to inflate an airbag.
And these chemical reactions happen when the car decelerates very quickly, as in a head-on crash, initiating the process of inflating the airbag.
Another chemistry involved is when the other chemical into which sodium azide falls apart is Na, or sodium. Sodium is a very reactive metal that will react rapidly with water to form sodium hydroxidethat is quite harmful if it got into your eyes, nose or mouth so with regard to these air bag manufacturers mix the sodium azide with other chemicals that will react with the sodium and, in turn, make less toxic compounds.
The pressure in the airbag, and hence the amount of NaN3 needed in order for the airbag to be filled quickly enough to protect us in a collision, can be determined using the ideal-gas laws, and the kinetic theory of gases allows us to understand, at the molecular level, how the gas is responsible for the pressure inside the airbag. Newton’s laws enable us to compute the force (and hence the pressure) required to move the front of the airbag forward during inflation, as well as how the airbag protects us by decreasing the force on the body.
The proper name for airbags is “Supplemental Restraint Systems,” and as the name suggests, they play a supplementary function in protecting the passengers. Airbags can only be fully effective when they are used in combination with seat belts.
- Web links