Unveiling the Hidden Limitations of Breathalysers: New Research Confirms that Some People are Unable to Provide.

Craig MacKenzie
Craig MacKenzie

Published: October 6th, 2023

6 min

Some people may be physically unable to use the current evidential breath analysis machines relied upon by police to gather proof of driving under the influence of alcohol or drugs, new research from the University of Sheffield indicates.

The new study challenges the norm that anyone failing to provide a breath sample at a police station is deliberately obstructive, questioning the fairness of 'failure to provide' charges.

Under the 1988 Road Traffic Act, anyone unable to complete a breathalyser test at a police station is automatically charged with Failure to Provide, which can have severe consequences for the offender, including driving disqualifications, a maximum possible sentence of six months imprisonment and an unlimited fine.

What did the researchers discover?

The general assumption of the police and the courts is that those who fail to provide a breath specimen are wilfully failing to do so, but evidence for this assumption is extremely thin.

The literature search revealed only four research papers on the current evidential machines. Each has difficulties because of small samples, little detailed analysis or commentary, and the risk of bias.

The researchers noted four characteristics that may impact a person's ability to give a breath sample: stature, age, sex and whether or not they smoke.

The researchers concluded:

Effects of stature

It is very clear from the BioBank data that shorter persons are at greater risk of being unable to provide a breath sample:

  • Whilst few men (0.3%) of average height or above are at risk, this increases eightfold to 2.6% for those below the 2nd percentile.

  • Women of average height and above are already more at risk than similar men at 1.3%, increasing threefold to 3.8% for those below the 2nd percentile.

  • Older women (70 and over) are particularly at risk - almost 1 in 10 of the shortest in this age group would be unable to use evidential machines.

Effects of age

Age is an important factor:

  • Risk (of being unable to provide a sample) approximately doubles with each decade from the 40s to the 60s.

  • Comparing the youngest with the oldest (40s vs 70s), the risk increases tenfold for men (0.16% vs 1.63%) and sixfold for women (0.65% to 3.83%).

  • There is an interaction between age and stature, with short, elderly persons least likely to be able to provide a sample, which is exacerbated if they are female.

Effect of sex

The sex of the person emerges as a critical factor:

  • Overall, nearly four times as many females would be unable to provide an evidential breath sample as males, although this difference decreases with age.

  • In comparisons based on age, stature or smoking status, sex remains an important factor, with women being more at risk than men in all circumstances investigated.

Effects of smoking

No previous study has investigated the effects of smoking tobacco despite its well-known deleterious effects on lung function. The present investigation confirms its relevance:

  • Smoking doubles the risk of being unable to supply breath samples in those beyond the 40s decade.

  • About 1 in 20 female smokers in their 60s could not supply breath samples.


This study implies that, overall, at least 1 man in 186 and 1 woman in 61 would be physiologically incapable of providing an evidential breath sample, and these figures can be approximately halved to 1 man in 87 or 1 woman in 32 if they happen to be daily smokers. Age increases risk, with people in their 70s being six times more likely to fail than those in their 40s. Concerning stature, the risk figures rise to 1 in 38 short men and 1 in 26 short women (i.e. below the second percentile of height), with increasing age further compounding this effect.

The UK has around 4,000 annual prosecutions for Failure to Provide under the 1988 Act. If, as the results imply, a percentage of the population is physiologically incapable of operating the extant machines, then some of these annual prosecutions may have had a wrong outcome - some individuals who should have received a penalty for driving under the influence of alcohol may have been acquitted when a different specimen would have proved their guilt, whilst other individuals who were not, in fact, over the legal limit may have been wrongly convicted of Failure to Provide simply because they were unable to use the machine.

It is impossible to estimate the actual number of unsafe convictions without detailed demographic information (age, sex, height, smoking status) regarding those who were prosecuted.

Is there an easy fix?

Correcting this situation would not require legislation but merely alterations to existing procedures, as the 1988 Act allows for a person to give an alternative sample if "the constable who required the specimens of breath has reasonable cause to believe that the device has not produced a reliable indication" or if "it is then for any other reason not practicable to use such a device".

It would be helpful if police forces were alerted that certain people cannot use the existing evidential machines and adopt a more flexible approach in allowing an alternative sample to be taken.

Our solicitors are familiar with this and other research, so if you face investigation or prosecution for any road traffic offence, please get in touch with us as soon as possible to ensure the best possible outcome.

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