Health issues at application of PIV
The presentation ‘Particulate Matter’ by Patrick N. Breysse and Peter J.S. Lees of the Johns Hopkins University provides an excellent introduction to this topic.
For many chemical substances, including some which are used for seeding flows, information about their hazard is available as safety data sheets in a structured format with topics such as:
- Hazards identification
- Composition/information on ingredients
- First-aid measures
- Fire-fighting measures
- Accidental release measures
- Handling and storage
- Exposure controls/personal protection
- Physical and chemical properties
- Stability and reactivity
- Toxicological information
- Ecological information
- Disposal considerations
- Transport information
- Regulatory information
- Other information
Each PIV laboratory should have available such data sheets for seeding materials as used by them for information of its personnel.
As an example links to such data sheets for Di-Ethyl-Hexyl-Sebacat (DEHS), a chemical substance which, due to its features (comparably long life time of droplets, but complete evaporation after long times), finds wide spread use at application of PIV in air flows are provided.
United States, manufacturer of DEHS:
Germany, specialist for aerosol technologies and user of DEHS:
At minimum all national standards and legal requirements must be met. It is recommended to check international standards possibly demanding higher protection levels for comparison as well.
Tracer particles as used for PIV
Many applications of PIV in air make use of liquid or solid tracer particles with diameters of 0.3 µm to 1.5 µm whereas applications of PIV in water make use of solid tracer particles with diameters of 20 µm. These diameters are determined as trade-off between adequate particle following behavior within the flow and high light scattering efficiency of the particles. PIV theory and experiment show that about 10 particles images should be present within an interrogation area in order to obtain reliable velocity data. From these data, together with the flow velocity and the cross section of the seeded flow, the minimum number of particles per second, resp. the minimum mass of the seeding material per second, as required for the PIV experiment can be calculated.
Whereas for liquid flows the tracer particles stay within the liquid and usually do not provide additional harm to the PIV user, for air flows it is necessary to assess any additional hazards due to the fact, that the seeding substances will be used as aerosol to form the tracer particles required for the PIV experiment
Hazard of aerosols
The hazard of such tiny particles to humans is quite obvious. For example, Chapter 10 of the Encyclopedia of Occupational Health and Safety
describes in details how aerosols will be inhaled by the human lung.
This means that the amount of aerosol inserted in the test facility of the PIV experiment must be minimized as far as possible, e.g.
- At production of the aerosol, by using a cascadable seeding generator to produce just that amount of aerosol as required for the experiment, and impactors to get rid of big particles, which are of no use for the PIV experiment
- At injection of the aerosol into the flow, by seeding only those stream tubes of the flow, which will pass through the PIV observation volume
- At the experiment, by using remote control (magnetic valves) for the air supply of the aerosol generator, to allow aerosol production only, if it is required for the ongoing PIV measurement
- By designing the experimental set-up in such a way, that the aerosol stays within an confinement, or, if this is not possible, to provide the personnel with appropriate breathing masks, to exhaust the seeded flow to the outside of the laboratory and to exchange the air within the laboratory immediately after the PIV experiment.
Test facility and laboratory
Contamination of the windows of the test section (affecting the quality of the PIV recordings), the walls of the test section and of screens and grids in wind tunnels due to the tracer particles must be minimized. Usually facility and application dependent solutions have to be developed based on the chemical substance used for seeding of the flow and the type of flow to be investigated.
In order to avoid any hazards, each PIV laboratory must strictly follow any technical and legal requirements related to seeding safety, in particular must have readily available all required technical and legal documents for information of its personnel, display the most important information in the laboratory or test facility, and train its personnel in regular intervals.
Contents provided by Markus Raffel and Jürgen Kompenhans, 20180327