How Long After Drinking Can You Use An Ignition Interlock?

October 18, 2018

Impaired driving remains a huge issue in the country. According to the Centers for Disease Control and Prevention, over 1 million drivers were arrested for driving under the influence of alcohol or other controlled substances in the United States in 2016. However, that accounts for just 1 percent of over 111 million self-reported incidences of drunk driving among adults estimated annually. About 29 people still die from crashes involving a drunk driver every single day.

Prevention efforts have been wide and variegated, ranging from litigation to community-based measures. Federal and state governments continue to enforce several laws to reduce alcohol-impaired driving, including 0.08 percent BAC legal limits and zero tolerance laws for drivers under the legal drinking age. Larger community efforts focus on education and health promotion measures.

Ignition interlock devices (or car breathalyzers) have become one of the most important and effective tools for preventing drunk driving. Data shows that ignition interlock devices reduce repeat DUI offenses by an estimated 70 percent for the period that they stay installed. Many states have begun implementing laws that require the installation of ignition interlock devices, even for first-time DUI offenses.

Using an ignition interlock device can potentially be confusing. Even when you are well-meaning and trying your best to follow the instructions and guidelines, you might still be wondering how long after drinking can you use your ignition interlock device. Let’s take a closer look at how ignition interlock devices work and when you can use them for successful breath tests.

What is an Ignition Interlock Device?

Ignition interlock devices generally comprise a mouthpiece, the device, and a cord connecting to the car’s ignition. Before you can start your engine, the device requires you to blow into it. If your blood alcohol concentration measures above a certain set limit (usually 0.02 percent), the device will prevent you from starting the car for a set period of time or until you provide a clean sample.

Along with this initial test to start your car, ignition interlock devices will also perform what’s called rolling retests. Periodically throughout your drive, the device will ask for another breath sample. If your breath sample exceeds the limit or if you do not provide the sample promptly, the device will warn you through a series of alarms (honking your horn, flashing lights) until you provide a clean sample or pull off the road and stop your engine. Rolling retests are designed to prevent you from using someone else’s breath sample to start your car.

Ignition interlock devices also log essentially every event, including test successes and failures. Many newer models also include global positioning systems that log the location and time of every test attempt. These logs are then sent to your monitoring authority, which can include the court, a parole or probation officer, or your driver’s license agency, either immediately or after every monthly calibration. Test failures or any signs of tampering can come with severe consequences, including fines, jail time, and increased IID periods.

How Do Ignition Interlock Devices Work?

When you drink alcohol, about 20 percent moves directly into your bloodstream fairly intact, while the other 80 percent goes to your small intestine before entering your blood vessels. Alcohol also happens to be highly volatile, meaning that it can easily evaporate given your body’s natural temperature. As your blood flows into and around your lungs, some of the alcohol evaporates and gets trapped in small sacs throughout your lungs known as alveoli. As you exhale, the alcohol stuck in your alveoli exit with your breath. Your breath alcohol level has a direct relation to the amount of alcohol in your blood. About 2,100 milliliters of alveolar air contains the same concentration of alcohol as 1 milliliter of your blood.

The modern ignition interlock device for cars works using a complex fuel cell system. The fuel cell comprises two platinum electrodes sandwiching an acid-electrolyte material. When you breathe into an ignition interlock device, one of the platinum electrodes oxidizes alcohol in your breath and breaks it down into acetic acid, electrons, and protons.

The electrons go through a wire leading to the other platinum electrode and an electrical current meter. The protons enter the lower chamber of the fuel cell to combine with oxygen and the electrons to form water. This creates an electrical current, which increases based on the number of electrons and water (a natural conductor). Essentially, the more alcohol in your system, the higher the electrical current level. Microprocessors within the device measure the electricity levels and calculate it into a blood alcohol concentration reading.

Alcohol and BAC

Blood alcohol concentration or content measures the amount of alcohol in your blood. It is expressed as a percentage of alcohol per every 100 milliliters of blood. For example, a BAC of 0.08 percent equates to 0.08 grams of alcohol per 100 milliliters of blood. BAC is the main quantitative unit of measure used by law enforcement to determine your level of impairment.

Alcohol gets broken down at a constant rate, but the effects and blood alcohol concentration can vary from person to person. Two people could drink the exact same drink at the exact same time and show different blood alcohol concentrations. Your BAC and the way you react to alcohol is affected by a huge range of environmental and individual factors, including:

    • Age – Generally, the older you are, the less effective your digestive system, making it much easier for your blood alcohol concentration to go up.
    • Genetics – The enzymes responsible for breaking down alcohol in your liver are determined by your genes. These enzymes can affect the speed at which alcohol gets metabolized.
    • Body size and composition – A smaller body mass naturally means that the alcohol has fewer places to go, making it much easier to concentrate within your system for longer. Individuals with higher body fat also generally have a higher tolerance for alcohol.
    • Liver – If your liver has been damaged or diseased or is generally unhealthy, it will have a harder time metabolizing the alcohol in your body, leading to a higher BAC and potentially causing further damage to the liver.
  • Food and water – Eating a meal before consuming alcohol and drinking water throughout can help to slow down the rate of absorption and allow for a slow, steady climb in your blood alcohol concentration.

Even taking these factors into account, there’s really no way to know your own BAC or how drunk you are without a breath testing device or a blood or urine test. Alcohol also conveniently hinders your own sense of judgment, meaning that you aren’t the most reliable judge of your own impairment.

The Standard Drink and Your BAC

A general rule of thumb states that it takes about one to two standard drinks to increase your BAC by 0.02 percent. That, of course, does not take into account the above factors that can affect the rate at which you process alcohol.

In the United States, a standard drink is considered any beverage containing 14 grams of pure ethyl alcohol. This might comprise:

    • 12 ounces of a regular (non-light) beer (5 percent ABV)
    • 8 to 9 ounces of malt liquor (7 percent ABV)
    • 5 ounces of wine (about 12 percent ABV)
  • 1.5 ounces of distilled spirits, including gin, rum, tequila, and whiskey (40 percent ABV)

Knowing what constitutes a standard drink can be helpful for pacing your own drinking and following your own health guidelines, but it’s also important to understand that every beer, wine, and spirit is different. Furthermore, not every server or bartender will necessarily pour the exact same amount.

When Is It Safe to Use Your Ignition Interlock Device?

There isn’t an easy answer to this question. The real answer is that you can use your ignition interlock device when you don’t have any alcohol in your system. The actual time that takes can vary based on the rate at which you metabolize alcohol and the amount of alcohol that you drank.

The general rule is that it takes one hour for your liver to fully break down one drink. That can be helpful in keeping track of your drinking and pacing yourself.  However, when you drink more than one drink per hour, the excess alcohol gets stored in your blood and muscle tissue until your liver can handle it. This inevitably leads to a higher BAC and more time required to bring that BAC down. A blood alcohol concentration of 0.08 should take about five hours to clear your system.

Can You Speed Up Alcohol Metabolism?

As mentioned earlier, eating a meal before you start drinking can help to slow down the immediate digestion of alcohol and absorption into your bloodstream, preventing sudden spikes in your blood alcohol content levels in favor of a steadier increase and drop off. However, this will not magically keep you from getting drunk altogether.

Despite various myths and old wives’ tales, there isn’t a way to speed up the process of breaking down alcohol in your system. Your body will burn off alcohol at an average of about 0.016 BAC per hour. Taking a cold shower or drinking coffee won’t do much of anything. Trying to vomit up alcohol likely won’t help either as alcohol can get absorbed into your bloodstream within 10 minutes of ingestion. Alcohol is not something you can sleep off either. Depending on how much you drank, it’s very possible to go to sleep and wake up still drunk. The only true way to sober up is to wait.

If you simply must drink, leave your car at home and consider alternative modes of transportation, whether that’s a cab, the city bus, or a rideshare service. If you’re drinking with friends, designate a sober driver.

If you are truly worried about failing your ignition interlock device test, your best bet is to just avoid drinking altogether. You don’t always need an alcoholic beverage to have fun. Consistently wanting to drive knowing that you’ve just had some drinks may point to more serious problems with alcohol. Don’t take the risk of drinking and driving.


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