Charging during spraying of liquids – Investigation of practice-relevant processes for the cleaning of small and medium-sized containers

Status:

completed 05/2021

Aims:

The process of spraying the highly conductive liquid water is considered to generate a strong charge. In explosion protection hazardous areas, the electrostatic ignition hazards emanating from water jets and water sprays must be evaluated by a thorough risk assessment. Thresholds of the liquid jets and the container dimensions are specified in the Technical Rule for Hazardaous Substances (TRGS 727) and the IEC TS 60079-32-1 and are intended for the prevention of electrostatic ignition hazards. The thresholds are based on measurements made 1983 by Post, L. et al. and corresponds with the performance limits of the liquid jets and the containers used at that time. It is unclear whether exceeding the thresholds represents an electrostatic ignition hazard. To keep up with technical development, the gap of knowledge needs to be clarified.

The aim of the project is to identify the parameters that maximize the process of charge separation and to determine the influence of the spatial limitation of the container. Measurement techniques that are potentially suitable for this must be checked for their suitability in water sprays and their limitations of use must be determined. The following question is to be answered on the basis of the measurements of electrostatic quantities:

Are there electrostatic ignition hazards when spraying water in explosion protection hazardous areas if the currently applicable thresholds for liquid jets and container dimensions are exceeded?

Activities/Methods:

Initially, measurements were carried out in a 1 m³ container, which was intended as a model arrangement. In consultation with the cooperation partners, the measurements could be extended to medium-sized containers with a volume of up to 44 m³. The safety-related evaluation was carried out on the basis of the measurements performed.

Results:

The result of this safety-related evaluation is that the currently valid thresholds for pump pressure of the liquid jets may be exceeded without a direct electrostatic ignition hazard.

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