Managing fluids at high temperatures presents a safety hazard as the fluid may come into contact with the engineer whilst the fluid is being sampled

Solar Thermal Fluid Sampling: Personal Safety and System Design Considerations

Christopher Wright | Global Group of Companies


It is critical that solar thermal fluids are routinely sampled to assess their condition in order to sustain normal operation. When sampling a fluid, an engineer needs to consider their own safety as well as the safest point to sample from a system.

A heat solar thermal fluid can operate up to 400°C


Parameter, unit

Typical values

Examples of a BDO-based HTF

Dowtherm A

Globaltherm® Omnitech

Therminol VP-1


Clear-to-light yellow liquid

A geranium-like odour

Operating range, 0C

15 to 400

Auto-ignition, 0C


Maximum film, 0C


Boiling point at 1013 mbar, 0C


Open flash point, 0C


Closed flash point, 0C


Density, kg/m3

1056 (at 250C)

Kinematic viscosity, mm2/s

2.5 (at 400C)

0.97 (at 1000C)


Typical physicochemical properties for commercially available BDO-based HTFs.

Managing fluids at high temperatures presents a safety hazard as the fluid may come into contact with the engineer whilst the fluid is being sampled. This of course needs to be avoided to safeguard personal health and safeguard employees. Indeed, the point from which the fluid is sampled from the system is also an important consideration. The safety considerations from these two perspectives are detailed in Figure 1 and considered in further detail below.

Personal protective equipment and safe sampling points in solar thermal power plants.



Personal protective equipment (PPE)

PPE is defined as any equipment that offers protection against hazards and are there to protect employee health and safety at work according to the Work Regulations Act 1992. Table 2 outlines the PPE that should be considered when sampling a fluid that is in operation as well as the potential risk and how this can be mitigated.


Health and safety consideration


How to mitigate the risk

Eyes, face, skin

Splashing of hot fluids and chemicals, as well as exposure to dust and gas

a. Wear safety spectacles

b. Wear a facemask to protects the skin

c. Wear coveralls to protect the skin


Deafening noise from operating equipment

Wear ear defenders


Any form of head injury such as bumping the head on stationary objects, hair entanglement or impact from falling or flying objects

Wear a hard hat


Vapours from the thermal fluid

Wear a respirator (half or full-face)


Hazards to hands and arms include abrasion, temperature extremes, cuts, contact and contamination with chemicals

a. When taking a live HTF sample it is recommended that heat-rated gauntlets are worn

b. Gauntlets need to be non-porous and to resistant the fluid penetrating the gauntlet

c. A cotton inner glove is also recommended as this serves as an additional layer against the gauntlet should it come into contact with a live solar thermal fluid and the cotton glove helps to stop moisture from pooling in the gauntlet


Much like hands and arms, the feet and legs also need protection from safety risks such as chemical splashes and falling objects

a. It is recommended to wear tight-fitting boots

b. Boots need to provide some heat resistance and must have a non-slip sole

c. Boots should also have a steel toecap to protect the toes and penetration-resistant mid-soles

d. Open-topped footwear, such as rigger boots, must not be worn when sampling as this type of fluid could potentially penetrate this type of boot


Table 2. Health and safety considerations when sampling solar thermal fluids.


Indeed, engineers must take appropriate precautions when entering potentially hazardous environments, such as concentrated solar power plants, and must be wearing PPE before taking a sample of the fluid. Health and safety considerations include how to protect the eyes, face, skin, ears, head, lungs, hands and feet.


Safe sampling point

The second aspect that has to be considered is the design of the system. When sampling a fluid it is imperative that a suitable sampling site is available – please see Figure 1. Ideally this needs to be a site that is outside so that vapours can escape to air. Also, any leaks would be easier to isolate in an open area as opposed to a closed and confined space. It is also important to identify a point where the fluid has a low pressure to avoid unnecessary sprays and leaks. This helps to further improve the safety of the sampling technique and safeguard the engineer. Lastly, the sampling site needs be part of the circulation so that the sampled fluid provides a representative sample and therefore a fair assessment of the fluid in the system.



The safe sampling of hot HTFs is a fundamental part of the training of engineers sampling solar HTFs. A commitment to safe sampling practices and training ensures that solar HTFs are sampled in a safe manner. Suitable sampling points need to be designed into the system that are outside and that provide a sampling point where a representative volume of fluid can be taken without the risk of the engineer being sprayed by hot fluid.

Figure 2. Solar thermal fluid sampling device.

Sampling needs to be performed by experienced engineers and the correct sampling techniques and equipment need to be used. Figure 2 shows a picture of a hot fluid sampling device that is routinely used by Global Heat Transfer [3]. This is echoed by Wagner [2] who stated that “Relevant regular maintenance services of the system components are necessary and to be carried out by experienced personnel to ensure trouble-free operation of the plant over a longer period.”



The author would like to acknowledge the writing support provided by Red Pharm communications, which is part of the Red Pharm company (please see @RedPharmCo on Twitter).


Research article

  1. Wright CI, Picot E. Safe sampling and handling of biphenyl diphenyl oxide heat transfer fluids. International Journal of Materials Chemistry and Physics 2 (1), February 2016; 9-14.
  2. Wagner WO. Heat transfer technique with organic media. In: Heat transfer media, second ed. Graefelfing, Germany: Maria-Eich-Straβe; 1997. p. 4–58 [Chapter 2].
  3. Wright CI, Picot E. Using routine sampling and chemical analysis of heat transfer fluid, early in a plant build, can help to extend the lifetime of CSP plants: A case study. Renewable Energy Focus 2015: Source:






About Chris Wright
Chris Wright is a research scientist, graduating from the University of Leeds in the UK with a BSc and PhD. His research focuses on the use and maintenance of heat transfer fluids in manufacturing and processing, which includes food, pharmaceutical, specialist chemicals and solar sectors.



The content & opinions in this article are the author’s and do not necessarily represent the views of AltEnergyMag

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