How Much May a Person Drink?

According to the provisions of the Road Traffic Act, 1989, it is an offence to drive a vehicle while under the influence of intoxicating liquor or a drug having a narcotic effect, or with a blood alcohol concentration of 0,05g or more per 100ml of blood.

The practical implication is that a blood alcohol concentration of less than 0,05g per 100ml blood provides no guarantee that one can drive a vehicle with the necessary skill, nor does it provide immunity against prosecution; with adequate proof one can be found guilty on the main charge, namely "drunken driving".

Blood Alcohol Content (BAC) limits:

Concentration of alcohol in blood: 0,05 gram per 100 millilitres (all drivers), professional drivers: 0,02 gram per 100 millilitres.
 
Breath alcohol content: 0,24 milligrams per 1000 millilitres (all drivers), professional drivers: 0,10 milligrams per 1000 millilitres.
 
Any person detained for an alleged contravention of any provision of this section shall not -

(b) during his or her detention smoke until the specimen has been taken, as the case may be.
 
No person shall refuse that a specimen of blood, or a specimen of breath, be taken of him or her.

Correlation Between Blood Alcohol Concentration & Clinical Features

0,00 - 0,05%

Most persons show no signs of abnormality at this level while some may already show signs of euphoria with a loss of the normal balance between inhibitions and impulses. Reaction time at the level of 0,05g% is already twice as slow as normal. Impairment of coordination is already evident at a level of 0,04g%.

0,05 - 0,10g%

There is further loss of inhibitions, impairment of the ability to be self critical, over-confidence, a decrease in ability to concentrate and clouding of judgement.Most persons have impaired muscular coordination at levels of 0,08g%. At 0,10g%, the reaction time is four times slower than normal.

0,10 - 0,15g%

There is further impairment of the ability to be self-critical, as well as emotional instability, memory lapses, and signs of ataxia, apraxia and agraphia. Reaction times are further delayed. Orientation with regard to time and place may be impaired.

0,15 - 0,25g%

Clinical features include ataxia, apraxia and agraphia, markedly decreased muscular coordination, a loss of orientation, emotional instability, impairment of balance and equilibrium, apathy and dullness with emotional outbursts, impairment of the normal response to painful stimuli, impairment of memory and possible memory loss.

0,25 - 0,35g%

The above-mentioned abnormalities are more pronounced.
Complete muscular incoordination is evident, together with apathy, loss of memory and complete loss of sense of orientation to time and place. Stupor is possible.

0,35g% and higher concentrations

Stupor is followed by coma, generalised anaesthesia and paralysis, depression of the vital centres controlling respiration and the cardiovascular system and body temperature, deep coma and death.

Diagnosis of Intoxication 

Sober

The individual is not, or is only minimally under the influence of alcohol and shows no signs of intoxication on examination.

Slightly intoxicated

The individual has a flushed face, dilated pupils and is euphoric with a loss of inhibitions.

Moderately intoxicated

The individual will, in addition to the above, display delayed pupillary reaction, in coordination of fine movements, Rhombergism, thick speech and a tendency to stumble when turning.

Strongly under the influence

The individual will now also have dilated pupils with very slow reaction, nystagmus, incoordination of movements, and a stumbling gait with exaggerated reactions when required to perform unexpected movements.

Very strongly under the influence

In addition to all the above-mentioned features, the face may be either flushed or pale, the pupils may be pinpoint or dilated, the person may be apathetic and show intellectual clouding and disorientation. Pronounced incoordination and pronounced Rhombergism are evident and vomiting may occur.

The Absorption of Alcohol in the Body

The absorption of alcohol in the mouth and oesophagus is minimal because of the rapid passage of the alcohol through these structures; approximately 20% of ingested alcohol is absorbed in the stomach and the rest is absorbed in the small intestine. Depending on the volume of alcohol ingested, a small quantity may reach the colon and be absorbed there.

There are a variety of factors which affect the rate at which alcohol is absorbed, and consequently, the rapidity with which the blood alcohol concentration rises:

i. If the mucous membrane of the stomach or small intestine is covered by mucus or food, absorption is delayed as the surface area of contact between the alcohol and the mucous membrane has been decreased.
ii. If the blood supply to the mucous membrane is increased as a result of congestion, inflammation or the ingestion of warm liquids, absorption will be increased.
iii. The rate of absorption of alcohol depends on the concentration gradient between the alcohol in the stomach and small intestine and the alcohol in the blood of the capillaries in the stomach and intestinal wall; the smaller the gradient, the slower the absorption.
iv. Absorption of alcohol in the small intestine may be decreased if gastric motility is reduced by medicines such as sympathomimetics, very high alcohol concentrations or in cases of nausea and shock.
v. Gastric motility and associated alcohol absorption is increased by the intake of large volumes of food and liquids.
vi. Gastric motility is increased in persons with gastritis and peptic ulceration.
vii. The presence of irritating substances in the stomach may cause pyloric sphincter contraction and a delay in gastric emptying, thereby delaying alcohol absorption.
viii. Psychological factors may unpredictably affect pyloric sphincter function and consequent alcohol absorption in the small intestine.
ix. Certain surgical procedures such as gastrectomy or gastro-jejunostomy will accelerate the passage of gastric contents into the small intestine with more rapid absorption of alcohol.
x. The higher the alcohol content of a beverage, the slower the absorption rate because of secretion of excessive mucus, pyloric sphincter spasm and suppression of gastric motility.
xi. Large volumes of beverage make contact with a large surface area of mucous membrane and also increase gastric motility with resultant faster absorption of alcohol.
xii. The presence of carbohydrates in beer delays alcohol absorption.
xiii. Alcohol absorption is accelerated where beverages contain gas such as carbon dioxide.
xiv. Warm beverages are absorbed faster than cold ones with faster alcohol absorption.
xv. Foodstuffs which are fatty in nature or which have a high protein or carbohydrate content delay alcohol absorption by reducing contact between the alcohol and the mucous membranes.
xvi. Fatty foods also delay gastric emptying with associated retardation of alcohol absorption in the small intestine.
xvii. Parasympathetic agents such as carbachol, pilocarpine, atropine and belladona increase gastric motility and relaxation of the pyloric sphincter, thereby increasing alcohol absorption in the small intestine.
xviii. Ingestion of levulose, nicotine and caffeine delay alcohol absorption.

Effect of Alcohol on Driving Skills

a. Visual functions

Even small doses of alcohol may cause longer eye fixation time, tunnel vision and defective attention switching.
The response time of both eye movement and accommodation may be lengthened and there is a significant reduction in tolerance to glare from the headlights of oncoming vehicles.

b. Information processing

Even with low blood alcohol concentrations, when more than one form of information input is presenting itself at one time the rate of processing is depressed significantly.
Alcohol impairs impulse conduction and transmission in the central and peripheral nervous systems; rapid information analyses and processing is delayed and this in turn delays prompt and appropriate decision making.

c. Judgement

Behaviour, judgement, self-control and depth of thought are affected with associated impairment of reaction times, accuracy of response speed judgement, and performance awareness.

d. Restraint and impulse

Alcohol disturbs the balance between restraint and impulse, frequently resulting in impulsive behaviour.

e. Muscular response

Alcohol produces a tendency to veer over the centre of the road and to take much longer to correct such a steering error; furthermore, even with low blood alcohol concentration levels, drivers tend to make too little or too much movement in negotiating corners.

High alcohol concentrations in the blood also increase the time required to apply the brakes as well as reducing the degree of control in the actual use of the brakes.