How Does A Breathalyzer Work In A Car?

October 13, 2018

According to the National Highway Traffic Safety Administration, 2016 saw 10,497 people killed in drunk driving-related crashes in the United States, which accounted for 28 percent of all traffic deaths in the country that year. Estimates suggest that roughly 29 people die every day from an alcohol impairment incident. That averages out to about one highly preventable death every 50 minutes.

Federal and state governments have taken a variety of measures in an attempt to prevent drunk driving deaths, injuries, and damage to property. These include:

  • Enforcing existing laws that set a 0.08 percent BAC legal drinking limit
  • Setting up sobriety checkpoints, particularly during holidays and weekends
  • Encouraging community-based efforts surrounding alcohol control and DUI prevention
  • Requiring drug and alcohol evaluation and treatment from those who do commit DUIs

Ignition interlock devices, more commonly known as car breathalyzers, have quickly become one of the most effective tools in preventing drunk driving. Studies suggest that ignition interlock systems reduce repeat DUI offenses by about 70 percent. Many states have created laws requiring the installation of IIDs for even first-time DUI offenses. Let’s take a closer look at how a breathalyzer works in your car.

What is an Ignition Interlock Device?

Ignition interlock devices are breath-test devices that connect directly to your car’s ignition system. A mouthpiece allows you to blow into the device, which measures your blood alcohol concentration. You have to blow into this mouthpiece every time you want to start your car. If your BAC exceeds a set limit (usually 0.02 percent), the device will prevent you from starting your car for either a set period of time or until you provide a clean breath sample.

Even after your car has started and you are on the road, the ignition interlock device will require periodic breath samples, known as ignition rolling retests. These retests ensure that your initial breath sample came from you and not from a third-party. If your breath sample registers above the limit, the device will log the infraction and cause your car to set an alarm (blinking lights, honking horn) until you either provide a clean sample or pull off the road and shut off your engine. The car will not shut itself off if you fail a rolling retest, which would more than likely cause an accident and hurt your engine.

Understanding Blood Alcohol Concentration

Blood alcohol concentration is simply a measure of ethyl alcohol in your blood. It is expressed as a percentage that connotes the amount of alcohol (in grams) per 100 milliliters of blood. For example, a BAC of 0.08 percent means that you have 0.08 grams of alcohol for every 100 milliliters of blood in your system. While blood is the primary (and arguably best) means of measuring your BAC, it can also be determined through your breath and urine.

Your liver is responsible for breaking down alcohol in your system. It’s generally efficient at doing its job, metabolizing about one drink’s worth of alcohol in one hour. However, you are likely consuming more alcohol than your liver can break down at once. Any excess alcohol gets stored in your blood and tissue, which increases your blood alcohol concentration.

The Standard Drink

According to the National Institute on Alcohol Abuse and Alcoholism, a standard drink in the United States contains about 14 grams of pure ethyl alcohol. In terms of what you’re actually drinking, that is equivalent to:

  • 12 ounces of a regular, non-light beer
  • 8 to 9 ounces of malt liquor
  • 5 ounces of wine
  • 1.5 ounces of distilled spirits and liquor (vodka, gin, whiskey, rum)

Of course, even within each specific drink type, the amount of alcohol can vary, and customary serving sizes can vary depending on who’s pouring your drink. It’s also important to understand that not everyone processes alcohol at the same rate based on a huge range of factors, including age, gender, and body weight.

How Ignition Interlock Devices Work

Ignition interlock devices operate similarly to modern breathalyzer devices used by police officers, and it all starts with the small sacs in your lungs known as alveoli. When you drink alcohol, it doesn’t completely break down and metabolize in your body. In fact, it ends up fairly intact in your bloodstream (in the form of ethyl alcohol).

Alcohol generally has a high volatility, meaning that it easily evaporates given your body’s natural internal temperature. As your blood flows into and around your lungs, the alcohol in your bloodstream evaporates into the alveoli. With enough alcohol (in its gaseous vapor form) concentrated in your alveoli, a breathalyzer test can detect and measure the amount of alcohol in your system with every breath to a fairly accurate amount. The general estimates suggest that every 2,100 milliliters of alcohol found in your breath contain as much alcohol as 1 milliliter of your blood.

The modern ignition interlock device operates using complex fuel cell technology. Each fuel cell comprises two platinum electrodes surrounding a porous acid-electrolyte material. When you breathe into the device, your breath passes into one of the platinum electrodes at one side of the fuel cell. The platinum reacts with any alcohol in your breath, oxidizing it and producing protons, electrons, and acetic acid.

The electrons move through a wire from one platinum electrode to the other and to an electric current meter. The protons move and combine with the electrons and oxygen to create water, which further helps to conduct the electrical current. Essentially, the more alcohol that gets oxidized, the stronger the electrical current. A microprocessor measures the level of the electrical current and spits out the blood alcohol concentration.

How Your Blood Alcohol Concentration Affects You

While it may seem like an arbitrary unit of measure, especially considering how people react differently to alcohol and being drunk, blood alcohol concentration can actually help accurately predict certain actions and behaviors and your general level of impairment.

0.02 percent (about 2 drinks)

You will experience general relaxation, some slight body warmth, and an altered mood. This is also when you will begin to lose some of your judgment. You will also have trouble dividing your attention and your visual acuity, including your ability to track moving objects.

0.05 percent (about 3 drinks)

You will feel good and begin to let go of your inhibitions, causing your behaviors to become much more exaggerated. Your alertness will go down, and your judgment will be greatly impaired. You’ll have trouble with small muscle control and coordination.

0.08 percent (about 4 drinks)

At this point, you are legally drunk. Your judgment, memory, self-control, and memory will be heavily impaired, and you will have problems with your muscle coordination, including your general balance, vision, hearing, and speech. If you tried to get behind the wheel, you’d be unable to steer properly, control your speed, or process information quickly.

0.10 percent (about 5 drinks)

At this point, your reaction time and coordination will deteriorate immensely. You’ll slur your speech, you’ll have trouble with coordination, and your general thought processes will be much slower.

0.15 percent (about 7 drinks)

You’ll have extremely reduced muscle control and coordination, and you’ll experience a major loss of balance. If you tried to drive, you wouldn’t be able to pay attention to the actual process of driving, and you’ll have significant problems controlling the vehicle, which will only be compounded by impairments to necessary auditory and visual processing.

Can You Trick Your Ignition Interlock Device?

Simply put, no. Rolling retests are the biggest precaution as they prevent you from having someone else blow into your car to start it or from blowing into your device when sober and then drinking when you’re on the road.

The modern ignition interlock device is a highly complex piece of technology. You are required by the courts to get your device calibrated and maintained once a month, ensuring that your IID is in proper working order. This also means that the vendor will likely notice any signs of physical tampering. The device itself will log any failed test and attempts at physical modification, like trying to unplug the battery. These logs are either sent immediately to the courts or during the monthly calibrations.

Tampering with your ignition interlock device is a serious crime with some severe penalties. You may be required to spend time in jail, pay exorbitant fines, and suffer a license revocation. The court may also extend your IID period, forcing you to keep your device installed for even longer. Don’t try to trick or cheat your ignition interlock device.

Prevent Drunk Driving

You are responsible for your own actions, whether or not you have an ignition interlock device installed. While it’s fine to enjoy alcohol in moderation, it’s important to plan ahead to make sure that you aren’t behind the wheel with alcohol in your system. As noted above, even BAC levels below 0.08 percent can result in physical impairments and problems with judgment. Some states have even begun to enforce laws that punish and discourage driving even with a BAC lower than 0.08 percent. According to the Governors Highway Safety Association, Utah will officially set its BAC limits at 0.05 percent as of December 30, 2018.

If you plan to drink, make sure that you plan ahead. That means:

  • Having a designated driver
  • Using a rideshare or taxi service
  • Spacing out your drinks or alternating between alcoholic and non-alcoholic drinks (this gives your liver enough time to break down the alcohol in your system to prevent high BAC levels)

Of course, there’s nothing wrong with staying away from alcohol altogether. You do not always need alcohol to have a good time.

Ignition interlock devices, enforcement of laws, and wider education go a long way, but preventing drunk driving also takes work at an individual level. Combining larger, community-based efforts with personal safety steps is the most comprehensive means of preventing alcohol-impaired accidents, now and in the future.



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