Odour safety factor

Phosgene cannot be detected by smell (see Section 3.1.3) at the generally accepted occupational exposure limit of 0.1 p.p.m. [43,1703]. Although the sense of smell undoubtedly acts as a natural safety detection warning system, the accepted odour threshold is approximately ten times the TLV-TWA. The odour safety factor (TLV/odour threshold) has been calculated as 0.11, and the material has been assigned an odour safety elassification "E" to suggest that less than 10% of attentive persons can detect the gas at a concentration corresponding to its TLV [43]. 

Solvent recovery handbook Table 10.6 Odour safety factor and safe dilution of common solvents (calculated at the solvent vapour pressure at 25 °C) ... 

Solvent TLV (ppm) Odour threshold (ppm) Odour safety factor Safe dUution... 

There are some circumstances where permanent ventilation cannot be installed to remove solvent fumes and the only method to make an atmosphere fit to breathe is by providing so much ventilation air that the solvent vapours will be diluted to a safe level. This will not necessarily produce pleasant working conditions since safe dilution is based on TLV and vapour pressure. A solvent (e.g. pyridine) with a very low odoiu threshold may have a nasty smell at a concentration well below its TLV as the values for odour safety factor indicate. 

The four main factors that affect the volume of use of a fragrance ingredient are its odour contribution to a fragrance, its stability and performance in the products to be perfumed, its safety in use and its cost. The first three factors are discussed in the chapters on perfumery, applications, safety and ingredient design (Chapters 7, 9, 10 and 15, respectively). The fourth factor, cost, depends on raw material availability and chemical process technology, which are discussed in this chapter. 

The ease of solvent handling also depends on odour, flammability, toxicity and environmental factors, some of which are again interlinked. The main factors governing the ease of handling are discussed separately in the chapters dealing with solvent flammability, safety, health and environmental considerations. The same applies to a certain extent to solvent stability. The industrial solvents discussed in this book are, as such, rather stable products. More reactive liquids such as olefins, acids, epichlorohydrin, many amines/ amides etc. are generally seen as reactants rather than solvents and are therefore not discussed further. 

Plants produce a variety of chemicals to survive attacks by microbial invasion (Grayer and Harbome 1994). These metabolites are either preformed in the plant (prohibitins) or induced after infection (phytoalexins). Since phytoalexins can also be induced by abiotic factors such as UV irradiation, they have been defined as antibiotics formed in plants via a metabolic sequence induced either biotically or in response to chemical or environmental factors. Many of these substances have been identified as flavonoids (Cowan 1999). Extraction of flavonoids and identification of their antimicrobial activity is useful not only for finding new drugs but also for obtaining natural products useful as food additives to improve the shelf life and safety of foods. In fact, an aliment can be deteriorated by spoilage bacteria, that cause and develop unpleasant odours, taste and texture, whereas foodbome pathogenic bacteria may cause diseases with flu-like symptoms such as nausea, vomiting, diarrhoea, and/or fever. Food additives with antimicrobial activity can be used to overcome such problems, but consumers tend to reject the present use of additives obtained by chemical synthesis flavonoids, as additives derived from natural products, can be a valid and preferred alternative (Cowan 1999). 

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