How are TNCO values determined?

The tar, nicotine and carbon monoxide (TNCO) contents in cigarettes are determined using a smoking machine, which smokes a cigarette in accordance with an established method. In The Netherlands and the rest of the EU European Union (European Union) the so-called ISO method is used, as set out by the European Commission. This makes it possible to check that products do not exceed the maximum permissible quantities of TNCO and to compare products. Cigarette smoke is permitted to contain a maximum of 10 mg of tar, 1 mg of nicotine and 10 mg of carbon monoxide when smoked in accordance with the ISO method.

Disadvantages of the ISO method

However, the measurements taken using the ISO method do not provide an accurate picture of the amount of TNCO that smokers actually inhale. The reasons for this include the fact that in the case of the ISO method the ventilation holes are not covered, whereas smokers (partly) close these holes with their fingers or lips. The TNCO contents measured are therefore lower than the contents inhaled by smokers.

The alternative measuring method

There is an alternative method that gets closer to the TNCO contents inhaled by a smoker, namely the Canadian Intense (CI) method. Using this method the smoking machine takes puffs on the cigarette faster, with a greater volume, and the ventilation holes are  taped over (see table). Measurements using the CI method produce higher TNCO values in cigarettes than measurements using the ISO method.

Figure. A test cigarette in the smoking machine.
There is a series of ventilation holes between the red lines. In the test according to the ISO method these holes remain open; in the test according to the CI method the holes are taped up.

Table. Specific characteristics of the ISO method and the Canadian Intense method, which are used to test cigarettes using a smoking machine. The bottom line provides an indication of the smoking behaviour of an average smoker.

Difference between TNCO values with and without holes in the filter

The presence of filter ventilation thins the smoke and thus the inhaled concentration of nicotine. In order to inhale the desired amount of nicotine smokers adapt their behaviour depending on the degree of filter ventilation, for example by inhaling more deeply, for longer or more often, or they even smoke more cigarettes.

In the case of a more intense smoking method or if the ventilation holes are closed off, greater quantities of harmful substances end up in the smoke. The increase is different for each substance as the combustion process is affected by the additional air drawn in. So for each mg of nicotine smokers are exposed to higher concentrations of, for example, tar, carbon monoxide, acetaldehyde and acrolein. These substances are harmful to health as they are toxic, carcinogenic and/or addictive.

Figure. The amount of nicotine determined by a smoking machine using the ISO method, compared with the amount of nicotine that a smoker actually inhales (based on Jarvis et al. 2001). The tobacco in all cigarettes contains the same amount of nicotine, but the amount of filter ventilation affects the values that the smoking machine measures. More filter ventilation results in lower values, whereas the amount of nicotine that a smoker inhales remains the same. Smokers thus get as much nicotine from a ‘light’ cigarette as from a ‘heavy’ cigarette by adapting their behaviour.

What does this mean for your cigarette?

The RIVM database includes the TNCO values, as provided by manufacturers, for cigarettes that were available on the Dutch market in 2015. Cigarettes with low TNCO values generally have more filter ventilation and are referred to by the media as ‘cheating cigarettes’. The TNCO values give an indication of the amount of ventilation in the filters rather than the amount of harmful substances that smokers inhale.