In some cigarette designs, diffusion of carbon monoxide out of a cigarette as the gases are drawn from their formation region towards the mouth end of the cigarette is more important than air dilution in controlling carbon monoxide mainstream delivery. The diffusion is a three-stage process: radial diffusion through the tobacco bed, diffusion through the paper, and diffusion away from the outer surface of the paper. Measurements have been made of the diffusion coefficient of carbon monoxide through paper, and the diffusion coefficient from the cigarette. The former has a value of 4.4 × 10
Vent blocking, the covering of the filter ventilation zone on a cigarette during smoking, is a potentially important aspect of smoking behavior. Various techniques have been used to assess the incidence of vent blocking, and widely different views have been expressed on its importance. Studies relevant to filter vent blocking have been reviewed with two overall objectives: to examine critically the evidence on the occurrence of vent blocking and to assess the effects of vent blocking on the smoke yield to the smoker. The reviewed studies fall into four main categories: (1) measurements of the incidence of filter vent blocking among smokers; (2) the observed effects of vent blocking on cigarette ventilation and machine smoke yields; (3) the effect of experimentally blocking vents on human smoke yields; and (4) simultaneous determination of vent blocking and smoke yield under human smoking conditions. Direct observation indicates that only 4% of smokers have their fingers in direct contact with the cigarette during puffing. Estimates of vent blocking incidence by lips during smoking range from 15-24% (saliva-staining technique) to up to 50% ('tar’ staining pattern technique) of smokers. For those smokers who do block the ventilation zone, a mean of 27% of the vents are blocked, and a maximum of about 50%. When the cigarettes are machine-smoked, the smoke yield increases in a highly non-linear manner as the blocked portion of the filter ventilation zone increases. This effect is also more pronounced at higher original filter ventilation levels. In contrast, smoking behavior monitoring techniques have shown that when the experimenter deliberately blocks the vent zone, the human smoker adjusts by taking smaller and fewer puffs. The blocked filter affects the yields of smoke components to the smoker less than it does smoking-machine measured yields. It is concluded that the incidence of vent zone blocking by fingers is quite low and relatively insignificant. The most reliable estimate for lip blocking is that up to 25% of smokers may cover the vent zone during at least one puff and for most smokers the coverage is partial. Ventilation zone blocking as it occurs in practice has only a relatively minor effect on human smoke yields compared to other smoker behavior factors. When a human smoker inadvertently partially or completely blocks the filter ventilation zone during smoking, he/she adjusts by taking smaller and fewer puffs. Because of these changes in puffing behavior during human smoking, predictions of the effects of filter vent blocking on smoke yields based solely on smoking machine yields are deceptive.
Vent blocking, the intentional or unintentional covering of the filter ventilation holes during smoking, is an aspect of smoking behaviour which could influence mainstream smoke yields. This study was designed to determine if, and to what extent, vent blocking by smokers’ lips occurs. Three groups of British smokers were asked to smoke their own brand of cigarette which was either an unventilated filter brand, or one of two brands containing different levels of filter ventilation. 300 Smokers were used in each group and the filter butts were collected. Approximately 10 filter butts per smoker were collected. The filter tipping papers were removed and treated with a ninhydrin solution. This stained the saliva imprint on the paper so that the mouth insertion depth of the cigarette could be measured. In addition, levels of retained nicotine on the filters were also determined. This, together with the known filtration efficiencies of the filter, enabled an estimate to be made of the mainstream nicotine yield of the cigarette during the smoking. The results indicate that British smokers have an average insertion depth of about 8.5 mm. 85 % of the ventilated filters examined showed no vent coverage by the smokers’ lips, 15 % showed some coverage. Based on the techniques used in the present study it appears that the presence or absence of filter ventilation zone coverage by lips is not reflected in the estimated nicotine yields to smokers. It is likely that other smoker behaviour factors have a more substantial role in determining nicotine yields within each cigarette delivery category.
SUMMARYInherently porous cigarette paper consists of an interlocking network of cellulose fibres interspersed with chalk particles. Spaces in this matrix are of the order of 1 J.Uil wide which is small compared to the paper thickness (usually 20 J.Uil to 40 J.Un). However, when cigarette paper is perforated after the paper-making process, e.g. by an electrostatic or mechanical process, the perforation holes are relatively large, usually having mean diameters of the same order of magnitude as the paper thickness.The total flow of air through perforated cigarette paper thus consists of two components: viscous flow through the porous structure of the paper inherent from the paper-making process, and inertial flow through the perforation holes. Since the air flow I pressure relationships due to these two components of flow differ and since the two components are additive, the total flow through perforated paper may be expressed as:where Q is the air flow (cm 3 min-1 ),A i~ the area of paper (cm 2 ) exposed to the flowing arr, P is the pressure difference across the paper (kilopascal), Z is the base permeability of the paper due to viscous flow through the spaces inherent from the paper-making process (cm min-1 kPa-1 or cORESTA unit),
The Smoking Behaviour Sub Group of the Cooperation Centre for Scientific Research Relative to Tobacco (CORESTA) was set up in 1996 with the aims of reviewing information relevant to smoking behaviour, publishing the reviews, identifying gaps in information and suggesting suitable studies. So far three reviews have been published by members of the sub group (1-3) and other reviews are in progress. One aspect of the subject that has become apparent to the sub group is that terms are used inconsistently in various papers on smoking behaviour. We therefore propose that the following terms and their definitions are used in the future.
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