Knowledge Base

Non-expert summaryVisual inspection is widely used in assessing and monitoring cleaning, sanitation and decontamination. This experimental study explored the degree of residual soiling on equipment surfaces that lies below the limit of visual detection. The goal of this study was to evaluate the limit of detection of visual inspections and establish evidence-based strategies to improve the implementation of this activity. 101 respondents completed a visual sensory test where each one looked at viewed 15 stainless steel and 15 white high density polyethylene sheets, clean or soiled with dry wheat flour, in a randomly generated order. They were asked if they could visually detect food residue on each surface and, if so, if the surface should be re-cleaned. They were also asked to answer this when they could touch the surfaces with a gloved hand. The impact of training, use of illumination, viewing angle and colour-contrast are quantified. The results provide a quantitative measure of the effectiveness of visual inspection, and factors than can influence this.