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Frequently Asked Questions (FAQ) - and other useful information!!
We are often asked similar questions
about Breathalysers - how they work, what the differences are, what the
different displays mean etc - so we've gathered together some of the more
typical phone enquires which you may find useful in deciding which device is the
best one for you!
INDEX
How a Breathalyser Works
When you drink, alcohol is digested in the stomach and
passes through the stomach wall into the blood stream. Broadly speaking,
neat alcohol (such as a straight whisky for example) drunk on an empty stomach
is likely to enter the bloodstream more quickly than, say, a milk-based cocktail
drunk after a fairly full meal. This does not mean you will become more
intoxicated from the straight whisky - just that the effect is likely to be felt
more quickly. Once in the blood stream it passes around the body and generates
the usual effects of alcohol on the body and brain. As the blood passes
through the liver it is gradually filtered from the bloodstream, reducing at
each "pass" until there is no longer any residual alcohol in the body. It
also passes through the alveoli in the lungs, and as you breathe and the oxygen
passes into the bloodstream, so does some of the alcohol in your blood
"evaporate" into the air in your lungs. It is this alcohol that a Breathalyser
is designed to measure. This is why it is necessary to measure deep lung air
when using a Breathalyser (see
"sampling" below),
and why it is important not to drink within 15 minutes of testing - otherwise
alcohol that remains in your mouth will be blown directly into the detector, at
far higher concentrations than is the case from alcohol that has passed through
the stomach, into the bloodstream, and into the air you breathe out. Clearly the
concentrations are often very low and the sensors have to be very sensitive to
detect the levels involved - hence why it is so important not to smoke or drink
before using them and why obtaining an accurate and consistent sample of air is
so important.
How to use a Personal Breathalyser
Although personal devices like the
AlcoSense
and
AlcoHawk
Precision can never replicate the absolute reliability
of something like a
Dräeger 6510 (see "Sampling Methods" and "Sensor
Types" etc below) they can be very useful when used
over a period of time to generate a "picture" of how you absorb alcohol.
Everyone is different, and factors such as the time taken drinking, the last
time you ate and your own metabolic rate can all affect quite dramatically the
rate at which alcohol is absorbed. It is impossible to simply equate 1 "unit"
per hour, or any other simplistic statistic, and then guess your resulting
level. A recent independent test carried out by the IOC newspaper group used one
of our Breathalysers to test a random sample of drinkers in Croydon one Saturday
night, and the results showed just how wildly wrong people were in trying to
guess their level of intoxication (for the full article,
click here)
Using a personal Breathalyser on a regular basis means the
user can build up a broad idea of the way in which they personally react, at a
time when they are not going to go anywhere near a vehicle, and can help them to
make sure they do not find themselves still over the limit "the morning after
the night before"!
The way to get the most from your Personal Breathalyser is
to use it regularly and use it to monitor the change in your level of
intoxication, rather than looking at a single specific reading.. Always wait at
least 15 minutes after drinking or smoking (or you can damage the sensor) and
then test yourself, trying to blow steadily and consistently (see
sampling below) so
that you blow the same each time. Take 3 tests, each approximately 2 minutes
apart, and compare the readings; if one is substantially different to the other
two, try once more. when you have three readings that are within a reasonable
difference of each other, take an average and wait 30 minutes - then test again.
Don't be surprised if the reading is not exactly the same every time - see
Sampling, Sensors
and Displays
below) - carry on testing every 30 minutes until you get a
zero reading. You may well find that the reading initially INCREASES,
between the first few tests and the next - this is because it is taking time for
the alcohol to be absorbed into the blood stream from your stomach. You will
also probably find that the level does not drop by the same amount every half
hour - this is one of the main reasons you bought your detector, to see how YOUR
body reacts and how long it takes to absorb the alcohol.
You can use the guide to
UK limits
below to get some idea of how your readings compare, but
if you intend to drive - do NOT drink!
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Sampling Method
One of the biggest differences between Breathalysers
is the way in which they sample your Breath. Professional, police-grade
Breathalysers such as the PT750
and UK-Approved
Dräeger 6510
measure an exact volume of air each time they are used -
usually 1.7 litres. They incorporate a flow meter to measure the air and a
physical gate to divert excess air once the required sample has been taken. This
means they can obtain accurate results every time irrespective of how the user
blows.
In contrast, "Personal" Breathalysers have varying methods of
regulating the sample taken - some better than others! The simplest
is the "Blow on" sensor -
Keychain style
and the compact "handbag" types like the
AL2500
all use this method, with a short sample of breath taken
by blowing at the unit. The AL2500 has a vent at the top of the unit
which the user blows through instead of onto but none are able to
take a full sample of deep lung air, but as a result the user must
expect a reasonably large margin error with such units. The
next "step up" is to make the user blow through a tube; this helps
to regulate the rate of sample, and enables a better standard of
measurement to be taken. The lower-priced units like the
Slim and
AlcoHawk
Precision
are all of this type while further up the range again
units like the
AlcoSense
and
AlcoHawk Pro
Digital incorporate a pressure sensor
which ensures a minimum air flow is maintained during sampling
(though none will limit the maximum sample that can be taken)
When used regularly by a single individual, who develops a
consistent blow of around 1.5 litres of air, the "blow-through" types can obtain
a reasonably good level of accuracy, however anyone considering using a
Breathalyser to test others should only really look at the
PT500, PT750
or 6510
or
similar in order to be certain that the sample is
identical and reliable every time.
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Sensor Types
Traditionally Breathalysers were all designed around a
device called a Fuel Cell. These are relatively expensive to
manufacture (often £200 or more just for the Fuel Cell) but are
highly accurate and reliable over a wide range and Breathalysers
certified for evidential use (known in the US as EBT's) use these
sensors. In order to produce a more economic device for personal and
home use various semi-conductor based sensors have been developed,
which use varying levels of software complexity to translate their
readings into equivalent values such as BAC%, mg/l and Microgrammes.
These sensors are more susceptible to drift (where the values
produced gradually vary as the unit gets older and is used more
often), saturation/contamination (for example if the user has been
smoking or drinking recently) and variations in temperature but for
general home use, provided some margin for error is allowed by the
user, can produce some perfectly acceptable results. Semi conductor
based sensors also have a narrower range of sensitivity and are more
complex to calibrate (see below) so for Employers or Enforcement
agencies, who must have a reliable and consistent reading over the
full range of use, only Fuel Cell, EBT-approved devices like the ACS
J5 and Dräeger 6510 are going to produce the required levels of
accuracy and reliability.
Users should also bear in mind that
the accuracy of a particular sensor quoted in the specifications has been
measured under strict laboratory conditions immediately following calibration.
Due to the variations listed above, and particularly the limitations of
sampling, it is unlikely that such specific accuracy is likely to be obtained on
a repeatable basis by the user "in real life" and sensor saturation with
alcohol, or contamination with smoke during a test, can quickly destabilise the
sensor software and lead to unreliable results. Anyone using a "personal"
Breathalyser should leave a substantial margin of error and take into account
general factors such as what and when they've been drinking - you cannot rely
solely on a Personal Alcohol Detector to determine your level of intoxication!
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Calibration
There are two methods of calibration
- dry gas, and wet bath simulation and all Breathalysers can only
remain accurate for so long before they need to be "reset" - or
calibrated - against a known benchmark concentration level of
alcohol. On the whole a personal detector will remain accurate
provided it is used properly, but once consecutive readings start to
drift by an unacceptable degree then it will need to be
recalibrated. Regular recalibration (roughly every 6 months) also
helps ensure the sensor stays within calibration range; once outside
this range, it cannot be reset.
Fuel Cell devices will generally
"hold" their accuracy for longer, however because they are usually in use in an
evidential environment most companies have them calibrated at least every six
months. Dry gas calibration can only be carried out on Fuel Cell devices and is
generally done at a single concentration level. Fuel Cells have a much
more linear detection range the semi-conductor based sensors and as such are
able to "predict" accurately both lower and higher concentrations from a single
calibration point. The advantage of dry gas calibration is that little or no
expertise is required to operate the equipment, and large-scale operators such
as the police are able to have their own in-house setup in order to regularly
check and calibrate their detectors. If the readings are not what you
expect, first try re-testing on several occasions to see if blowing technique is
an issue - see "how to use a personal Breathalyser" and "sampling methods"
above/
Semi-conductor devices on the other hand are calibrated
using wet-bath simulators, which is a device containing water, mixed with pure
alcohol at a precise level and heated to an exact temperature. A minimum of two
are required, and a Customs & Excise licence is required to purchase and store
the materials. Semi-conductors have a much narrower, and less linear,
range than fuel cells and so are usually calibrated at two points - a "low"
level and "high" level just above and below the expected key point of use - in
the UK, either side of the drink drive limit of 0.08 BAC%. The software in the
unit then compares these two fixed points from the air supplied by the wet bath
simulator and uses them to forecast other readings up and down the range. The
problem however is that it is relying on the software to predict the results,
and the non-linear nature of the sensor means it can only do so to within
certain limits, particularly at very high (more than 0.20 BAC%) or very low
(less than 0.02 BAC%) levels. For personal use, as a general indicator of
changes in the level of intoxication, semi-conductor based Breathalysers are
very useful devices but users cannot put too much store by any one specific
reading and must allow reasonable margin for error (see Sensor Information
here). To have a Breathalyser calibrated, see our order page
here.
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Displays and Measurement Units - BAC%, mg/l etc
There are three basic types of
display; LED's that show a range of values (like the SafeDrive
Keychain and CA1000) and either backlit LCD or Digital LED devices
that produce a digital reading. These displays generally show
three digits, however if calibrated to display the results in BAC%
one digit is always a zero (The UK limit is 0.08%, so even someone 5
times over the UK limit would still only register a reading of
0.40%). Alternative forms of measurement include mg/L (where the
limit is 0.40), mg/100ml (limit 80mg - this is the measurement
reference used by UK police until around 5 years ago) and
Microgrammes (the current Police standard, where the UK limit is 35
microgrammes)
Most "Personal" Breathalysers sold
in the UK display their results in BAC%, which is the standard most commonly
used in the US. The problem with this standard is that between zero and the
drink-drive limit of 0.08, the unit only displays a change of 8 "steps" of
0.01%, and approximates the values in between. For example, 3 tests taken 2
minutes apart may produce sensor values of 0.045, 0.050, and 0.055 - but all
would display as 0.05. On a unit displaying mg/100ml however, the full reading
would be displayed in full as 045, 050 and 055 allowing the user to make a more
informed decision. Bearing in mind the comments made above with regard to
sampling, it also gives the user more feedback as to the consistency with which
they are using the Breathalyser.
Certain websites claim that their
devices actually "read" a sample in BrAC - "Breath Alcohol Content". Clearly
this is nonsense - every sensor merely outputs an electrical signal, which is
then converted by the software in the unit to correspond to an accepted value of
measurement. Whether that is BAC%, mg/L, mg/100ml or Microgrammes is irrelevant
- different standards have been adopted by different countries and all are as
valid as each other provided the device is used correctly and properly
calibrated at the time. It is the same as weighing an apple in grams,
pounds, kilos, stones etc - the apple still weighs the same!
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Approvals - UK & USA approval standards, ASD's vs EBT's
In the UK, the Home Office ONLY approve devices for Evidential use, and as yet only Fuel Cell, fixed-volume sampling devices like the
6510 have so far been approved. In the USA, the Department of Transportation (DoT) approve two types -
ASD's (Alcohol Screening Devices) and
EBT's (Evidential Breath Testers). Again, only Fuel Cell devices have been approved in the US as EBT's, but there are a substantial number of semi-conductor based devices that have been approved as ASD's, including the AL5000, CA2000, AlcoMate Pro S etc. All these devices are the blow-through type (see above) and all sample for at least 3 seconds, but users must remember that the US DoT approval is only limited to their ability to detect the PRESENCE of alcohol. They are NOT assessed for their ability to accurately measure a specific alcohol LEVEL, in the way that an EBT is. They are expected to be used only for general screening, with anyone that indicates anything over zero being re-tested using a properly approved EBT. This makes them a very useful "morning after" device for home use and for measuring the comparative rate that an individuals' body metabolites the alcohol but users must realise that something costing in the region of £50 - £100 is not going to reproduce the level of specific accuracy and reliability of an EBT costing £700 or more.
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Limitations of Personal Breathalysers (non-EBT's)
All "personal" Breathalysers (ie. those based around semi-conductor sensors) are either non-approved, or at most approved in the USA as Alcohol Screening Devices (ASD's) and as such the US DoT that approves them advises
"The exact alcohol content in the blood of the test subject cannot exactly be determined by using an Alcohol Screening Device. Only an Evidential Breath Tester or Blood test can be relied upon for accurate determination. Do not Drink and Drive". In addition, the following limitations must be considered: -
The result can be affected by variations in Blow Technique & Temperature -
The unit's calibration can only be certified when issued; it cannot be guaranteed over time and can become contaminated by a single use involving smoke or excessive mouth alcohol (saturation) -
The test reflects only the levels detected at a single point in time and levels of intoxication will often peak sometime AFTER the last drink. -
Regular use of the detector over a period time (see
"how to use a personal Breathalyser")
is the best way to use a Breathalyser and learn how alcohol affects the individual person. This can then be used, along with a suitable safety margin, to help ensure the user is clear of alcohol before undertaking critical tasks or driving. -
Personal Breathalysers can only be used to give an indication of the possible presence of alcohol in the blood. The user must NOT rely solely upon the indications provided by this equipment and must use his/her own judgment, taking all factors into account, to determine whether it is safe and/or legal to operate a vehicle.
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UK Limits
The legal limit for alcohol levels in the body while in control of a vehicle vary from country to country and can be defined by several different standards, the following of which are the most common: -
35 microgrammes - as used by professional Breathalysers such as the Dräeger 6510, XT & 7410 -
80 mg/100ml - as displayed by the AlcoHawk Pro, CA2000 Pro
and AlcoScan 6000 Pro -
0.40 Mg/L - as displayed on the AL5000 Pro -
0.08% BAC - used by the majority of "consumer" Breathalysers
For those involved in the transportation industry, much stricter limits apply (for full details see
here) but in principle aircrew, maritime and railway employees are all subject to a limit that is just one quarter of the above, ie: -
9 microgrammes - as used by professional Breathalysers such as the Dräeger 6510, XT & 7410 -
20 mg/100ml - as displayed by the
AlcoHawk Pro, CA2000 Pro and AlcoScan 6000 Pro -
0.10 Mg/L - as displayed on the AL5000 Pro -
0.02% BAC - used by the majority of "consumer" Breathalysers
At these low levels only Fuel Cell Evidential Testers are able to provide accurate readings. Although the mg-based Pro S & CA2000 Pro may provide enough resolution to be useful as a general to those working in these industries, they should not be used for testing employees as the results at these levels cannot be relied upon. BAC-based devices are reading to within just two places of a zero reading and are therefore ineffective at these levels.
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