Drink Drive limit

[MK Shrimper]

As Scotland has reduced the limit from 80mg/100ml to 50mg/100ml, which makes it close to the limit if you drink even 1 pint or 1 glass of wine, do you think England should follow suit?

Personally I think it should be as close to zero as you can make it (taking into account naturally occuring alcohol) - for NR the limit is 30mg/100ml and I've known of people to get sacked if they've had a heavy night BUT driven to work legally.

Thoughts?

 

[Benfleet A1]

Zero, if I get tested at work and anything is found then I'm down the road, simple as that.

 

[RobM]

It is not possible to have a limit of zero for the following reasons.

Metabolism of sugars in the body produces alcohols, there and hundreds of types. So, for example, if you have a sugar in your morning coffee and then drive, you would be "over the limit". That's plainly daft.

Now, having worked in nationally accredited laboratories for 37 years, you can take the following as gospel.

Here we go.

1. Limits of detection of the test. Measurement of anything is restricted by this. If, for example, you wanted to measure the width of your lounge for a carpet to be fitted, you wouldn't set the milometer on your car to zero then drive the same distance as the lounge width. You'd get a reading of zero, which it isn't because the milometer can only measure to the nearest 0.1 therefore, the most accurate reading you can use would be <0.1 kilometres. The limit of detection for our alcohol test might be 1.

2. Repeatability of the test. At school science lessons this was "experimental error". The alcohol test may have a repeatability of (say) plus or minus 2. So, if you test a certified standard with a value of 100 ten times , you may will get readings of between 98 and 102. Therefore, a pure distilled water sample with no alcohol whatsoever could give a result of 2.

3 Reproducibility. Same sample, different technician, different equipment. The reproducibility limit may be plus or minus 5.
A way to illustrate this - get a piece of string, about 15 cm long and measure it 10 times with a school ruler. Now give that string to 5 other people and get them to do the same (recording the measurements), You will find a spread of results.

So, to conclude, a pure water sample with a value of zero could give a valid result of zero to 6.

Bearing in mind all that, a limit of 10 would safeguard those who have never consumed alcohol or sugar ever!

(The figures I have used are purely arbitrary, I have not mentioned the units of measurement, in this illustration they are irrelevant).

I hope you're still awake!

 

[Benfleet A1]

It is not possible to have a limit of zero for the following reasons.

Metabolism of sugars in the body produces alcohols, there and hundreds of types. So, for example, if you have a sugar in your morning coffee and then drive, you would be "over the limit". That's plainly daft.

Now, having worked in nationally accredited laboratories for 37 years, you can take the following as gospel.

Here we go.

1. Limits of detection of the test. Measurement of anything is restricted by this. If, for example, you wanted to measure the width of your lounge for a carpet to be fitted, you wouldn't set the milometer on your car to zero then drive the same distance as the lounge width. You'd get a reading of zero, which it isn't because the milometer can only measure to the nearest 0.1 therefore, the most accurate reading you can use would be <0.1 kilometres. The limit of detection for our alcohol test might be 1.

2. Repeatability of the test. At school science lessons this was "experimental error". The alcohol test may have a repeatability of (say) plus or minus 2. So, if you test a certified standard with a value of 100 ten times , you may will get readings of between 98 and 102. Therefore, a pure distilled water sample with no alcohol whatsoever could give a result of 2.

3 Reproducibility. Same sample, different technician, different equipment. The reproducibility limit may be plus or minus 5.
A way to illustrate this - get a piece of string, about 15 cm long and measure it 10 times with a school ruler. Now give that string to 5 other people and get them to do the same (recording the measurements), You will find a spread of results.

So, to conclude, a pure water sample with a value of zero could give a valid result of zero to 6.

Bearing in mind all that, a limit of 10 would safeguard those who have never consumed alcohol or sugar ever!

(The figures I have used are purely arbitrary, I have not mentioned the units of measurement, in this illustration they are irrelevant).

I hope you're still awake!

Wow, I needed that after a night shift :smile: Ok, clearly you know what you are saying, what would be the level as close to zero limit that you could get to that would give a accurate reading?

 

[Pubey]

As close to zero as is possible.

 

[RobM]

As close to zero as Pubey says.

The lowest limit in the above scenario would be;

Limit of detection + reproducibility. In our case, 6. If the result was zero, it would have to be reported as <1 because in reality it could be ( say) 0.4.

When I used to test the lead content of unleaded petrol, the limit of the test was 0.001 grammes per litre so if the displayed test result was zero (as in 0.000) we were compelled to report <0.001 because even if the real content was 0.00000001, it's greater than zero.

Heavy subject, I hope I have explained it adequately.

 

[GrumpyBlue]

As close to zero as is possible.

I would agree with this

 

[Jim Levenstein]

whatever allows you to have one pint

 

[Pubey]

whatever allows you to have one pint

Even my G&T nightcap?!

 

[Yorkshire Blue]

Even my G&T nightcap?!

Easy on the tonic.


The issue here isn't so much the one pint that night, but the reading the following morning after maybe 4 or 5.

 

[prawntobewild]

I just take the view that if it's likely I could be driving anytime soon then don't have a drink .Small readings may be present due to medication or even mouthwash .
Even if an incident occurs that is not your fault then the element of doubt is reduced as far as possible.
As a guy with a young family who may have to drive at anytime I have been teetotal for over 10 years so no problem for me but you should never really get to the "I should be ok if I drink this one .. I hope" stage.

 

[Shrimper2thecore]

I think we are better off spending time and effort on getting the nation to start obeying the limit we do have, rather than changing it.

Those that ignore it now, will still ignore it, and so the problem hasn't actually been addressed.

 

[RobM]

Prawn - the alcohol in a mouthwash would obviously influence a test. The way I understand it (and happy to be corrected) is - a fail breath test at the roadside is repeated 20 minutes later because any alcohol in the mouth may not be in the blood, reason as you have described. So, it's possible to fail a breath test (they are only an indication, not accurate) and be well under the blood test limit, which is a far more accurate test.

Just an idea - the punishment for any alcohol in the blood has a sliding scale of punishment; e,g, a blood test reading multiplied by 3 for a fine even if under "the limit". So a blood reading of 22 (for example) means a £66 fine but no ban or insurance problem as it's under the current 80mg/100ml limit.

 

[Yorkshire Blue]

Prawn - the alcohol in a mouthwash would obviously influence a test. The way I understand it (and happy to be corrected) is - a fail breath test at the roadside is repeated 20 minutes later because any alcohol in the mouth may not be in the blood, reason as you have described. So, it's possible to fail a breath test (they are only an indication, not accurate) and be well under the blood test limit, which is a far more accurate test.

Just an idea - the punishment for any alcohol in the blood has a sliding scale of punishment; e,g, a blood test reading multiplied by 3 for a fine even if under "the limit". So a blood reading of 22 (for example) means a £66 fine but no ban or insurance problem as it's under the current 80mg/100ml limit.

Insurers would categorise them as a higher risk and therefore charge them more.

 

[dloman]

Think I read somewhere today a piece from one of the pressure groups on drink driving that realistically the lowest it could be would be 20 due to the reasons others have stated and allowing for errors in reading.

 

[dloman]

I think we are better off spending time and effort on getting the nation to start obeying the limit we do have, rather than changing it.

Those that ignore it now, will still ignore it, and so the problem hasn't actually been addressed.

Exactly this , someone who ignores the limit when it is 80 will still do if it is 50 or 20.

 

[RobM]

Agree. It's like using a mobile when driving - if people never get stopped, the punishment is no deterrent.

 

[RobM]

Insurers would categorise them as a higher risk and therefore charge them more.

Hmmm. any more than a driver who does 69 mph on a motorway where the limit it 70?

 

[MK Shrimper]

Exactly this , someone who ignores the limit when it is 80 will still do if it is 50 or 20.

I agree, but how about those who accidentally go over the 80 limit? Maybe if you're in a pub and the law is 20 (ie, nothing) you wouldn't drink any alcohol at all.

Perhaps the cultural shift will be if you're going out and driving, you don't have just the one, you have none at all.

 

[Yorkshire Blue]

Hmmm. any more than a driver who does 69 mph on a motorway where the limit it 70?

You don't get fined for 69mph on a motorway (except if the cones are out).

The insurers would if you've had to pay a motoring fine in the past 5 years and if you have bump up the premium accordingly.