Patrick Horan

In a groundbreaking decision with far-reaching implications for drink driving cases across Ireland, a ruling at Clonmel Circuit Court has determined that defendants must be allowed to inspect the Evidenser breathalyser machines in Garda stations used to prosecute them.

Judge Catherine Staines’ judgment marks the first time an Irish court has ordered full access to both the hardware and software of these devices. 

The judgment was delivered at Clonmel Circuit Court on 7 March 2025. The defendant was represented by Mr David Staunton BL.

The case

The landmark ruling came in the case of DPP v PJ Flanagan [A2023/3543], where the defendant appealed his District Court conviction for driving with excess alcohol.

Mr Flanagan was charged after an Evidenser machine in Thurles Garda Station recorded his breath alcohol concentration at 66 micrograms per 100 millilitres. The limit is 22 micrograms.

Mr David Staunton BL, representing Mr Flanagan, made an application to inspect the Evidenser machine that produced the evidence against him. 

This included a request to examine both the machine’s hardware and software — something the State had fiercely resisted in all previous cases.

Dr Jordan’s expert testimony on breathalyser reliability

Central to the appeal was the testimony of Dr Mark Jordan, a consultant forensic engineer, who provided detailed evidence on why a full forensic examination was necessary to verify the reliability of these machines.

He said that a visible inspection didn’t allow for one to establish the forensic integrity of the machine: “It doesn’t tell you what’s going on in the machine”.

Dr Jordan outlined several critical concerns in his report.

Software transparency issues

The software governing the Evidenser’s operation was not publicly disclosed, making it impossible to independently verify whether it functioned correctly. 

Dr Jordan emphasised that accessing this software was essential to test the “forensic integrity” of the devices.

Inconsistent error margins

While the Evidenser applies a 17.5 per cent reduction to a suspect’s breath test results (as a safety margin), Dr Jordan noted that this same reduction was not applied to the calibration and control tests performed on the machine. 

This inconsistency raised questions about the reliability of the results. What was the basis of the 17.5 per cent margin of error? 

Calibration and test concerns

During Mr Flanagan’s breath test, the calibration check showed a reading 11.1 per cent lower than expected. Dr. Jordan pointed out that this error, while within acceptable limits, indicated potential issues with the machine’s accuracy.

Real-world examples of technology failures

Dr. Jordan pointed to significant real-world examples where technology had been compromised or failed:

• the Volkswagen emissions scandal, where software was reprogrammed to show false readings;
• Boeing’s aircraft software issues that overrode safety features; and
• electronic voting machines that proved vulnerable to errors.

No independent verification

Unlike laboratory blood and urine tests performed by qualified scientists, Evidenser machines are operated by gardaí who aren’t trained to verify the scientific principles behind the results they produce.

The defence arguments for inspection

Mr David Staunton BL said that Mr Flanagan was entitled to inspect the Evidenser on the basis of:

• the Supreme Court case of Oates v Brown [2016]; and
• the EU Disclosure Directive 2012/13/EU.

The State’s arguments against inspection

The State strongly opposed the inspection request on several grounds:

• Relevance concerns: They argued that an inspection would be irrelevant because the machine had tested Mr Flanagan’s breath nearly three years ago.

• Machine changes: The State claimed the Evidenser had been moved between stations, used hundreds of times, and had its gas cannister components replaced since Mr Flanagan’s test.

• Potential damage: They expressed concern that removing parts would compromise the machine, valued at €12,000.

• Commercial sensitivity: The State argued they couldn’t provide the software as their agreement with the supplier precluded sharing this information due to commercial sensitivity.

Dr Jordan’s counter-arguments

Dr Jordan countered these objections, stating:

1. The machine would be the same device with presumably the same software.
2. If moving the machine between stations or normal wear and tear could affect its accuracy, this actually supported the need for forensic examination.
3. The machine would not be damaged during inspection and could be recalibrated afterward.
4. Software access was essential to proper examination of the device’s reliability.

Judge Staines’ landmark decision

After hearing evidence from both sides, Judge Staines ruled in favour of allowing the inspection, citing several key legal principles:

• Fair procedures: The judge emphasised that fair procedures require that a person accused of drink driving must be free to contest breath test results just as they would be free to contest blood or urine analyses.

• Supreme Court precedent: Judge Staines heavily relied on the Supreme Court decision in Oates v Browne [2016], which established that since breath specimens don’t permit a portion to be retained for independent testing, defendants must have the right to inspect the machine that analysed their breath.

• Rebuttable presumption: The judge noted that without allowing inspection of the Evidenser, it would be “impossible to rebut the presumption that a printout from the machine was sufficient proof of its contents”.

• EU Disclosure directive: She referenced the EU Disclosure Directive 2012/13, which entitles defendants to access all material evidence.

Addressing the State’s claim that they couldn’t provide software access due to commercial agreements, Judge Staines stated:

To the State argument that their agreement with the supplier precluded sharing this information due to commercial sensitivity, Judge Staines was specific. She said that “it is within the power and control of the MBRS when negotiating a contract to require that access to software be made available in limited circumstances to an accused person’s engineer with strict conditions requiring a prohibition on the use of that information by that engineer”.

She concluded that the defence should be allowed to test the forensic integrity of the Evidenser, including accessing both its hardware and software.

Wide-ranging implications for drink driving cases

This decision could transform how drink driving cases are prosecuted and defended across Ireland:

• defendants now have a stronger basis to challenge breathalyser evidence;
• the Medical Bureau of Road Safety may need to ensure software access is included in future contracts;
• the State will need to demonstrate greater transparency around these machines; and
• the accuracy and reliability of all Evidenser machines may come under increased scrutiny.

The ruling underscores a fundamental principle articulated by Judge Staines, who concluded her judgement by saying: “Clearly there is a huge public interest in the successful prosecution of drink drivers. It is essential that the breath testing apparatus being used in these prosecutions withstands forensic scrutiny if so required by an accused person.”

• Patrick Horan is a former Garda who now practices law as managing partner of Patrick Horan Solicitors, specialising in the defence of drink and drug driving prosecutions.