What amount of fibres would normally come away from the seat normally in "normal" use??
Persistence of trace evidence such as hair and clothing fibre
https://www.fbi.gov/about-us/lab/for..._review02.htm/
Transfer and Persistence of Hairs
The primary mechanism for the transfer of trace evidence is described by the Locard Exchange Principle (Locard 1930). Although there will always be a transfer of trace evidence, in some instances, the material exchanged may be too small to detect or may be rapidly lost. Numerous authors have addressed the transfer and persistence of fibers in forensic cases, including Kidd and Robertson 1982; Pounds and Smalldon 1975a, 1975b, 1975c; and Robertson et al. 1982.
These authors investigated the mechanisms involved in the transfer of textile fibers and the persistence of the fibers after the transfer occurred. Although these studies primarily involved textile fibers, wool fibers were used in these studies; therefore, the results of these studies also apply to human hair. These authors found that the number of fibers transferred depended on the amount of pressure involved in the contact and the duration of the contact.
With regard to persistence, these authors found that the nature of the recipient garment, the size of the transferred fiber, and the movement of the recipient garment had a dramatic effect. If the garment containing transferred fibers was worn, most fibers were lost rather quickly (within a few hours). If the garment containing transferred fibers was held in a fume hood, the rate at which fibers were lost was much lower.
Gaudette and Tessarolo (1987) stated that many of the variables affecting fiber transfer and persistence were also important in hair transfer and persistence. In order to document some of these variables, they conducted several experiments on hair transfer. They identified two mechanisms of hair transfer: primary and secondary transfer.
Primary transfer can be either direct (from person A’s scalp to another location) or indirect (from person A’s scalp to person A’s environment and then to another location). Secondary transfer is an indirect transfer (from person A’s environment to person B’s environment to person C’s environment). The authors demonstrated that secondary transfer of human scalp hair can and does occur in casework situations and that persistence of the transferred hair is similar to that previously found for fibers by Pounds and Smalldon (1975a, 1975b, 1975c). Robertson and Somerset (1987) conducted a similar study on persistence and found comparable results; that is, most transferred hairs are lost with normal wear after about three hours.
Quill (1985) recovered 81 hairs from his clothing over a 31-day period. Of the hairs that were suitable for microscopic comparison, all had been transferred from family members. Quill concluded that for a foreign hair to be present on clothing, close personal contact is required. Simons (1986) found that although most hairs are removed from clothing during the laundering process, some hairs do remain on clothing and hair transfers can occur as a result of the laundering process.
Peabody et al. (1985) investigated the shedding of hairs into various types of headgear. They found that the number of hairs shed varies with the type of headgear worn and with the individual. They also noted the importance of collecting head-hair combings, because the nature of the hairs shed in their study were more similar to the naturally shed hairs encountered in combings than to the hairs encountered in plucked, known head-hair samples.
Based on these studies, it can be concluded that it is reasonable to find hair evidence in forensic cases. Hair is ubiquitous in the environment and, therefore, may be transferred during a crime. However, it is imperative for proper and timely collection of evidentiary materials, including known hair samples, to occur if hair examinations are going to be valid, reliable, and meaningful.
