A sophisticated medical hardware requires special reliability. It is the hardware which dialysis centers are equipped with, to treat patients suffering acute and chronic kidney disease. Recently ZANDZ Technical Center has received following question: How to make the lightning protection for a dialysis center? Let us consider the solution we provided below.
Example of calculation for the medical care dialysis center
Object: Medical dialysis center.
Figure 1 - Object dimensions.
Perform calculations of the earthing and lightning protection system for the medical care dialysis center.
Protection of the buildings and structures against lightning discharge is provided by using the lightning arresters. The lightning arrester is a device which is elevated over an object and through which the lightning current goes into the ground bypassing the protected object. It consists of an air terminal which is specially designated to arrest the lightning discharge, a conductor and a ground terminal.
The set of arrangements ensuring compliance with the lightning protection requirements of the medical dialysis center is based on the following solutions:
1. The lightning protection is made in accordance with Electrical Installations Code (EIC), Rev. 7., SO 153-34.21.122-2003 "Guidelines for making the lightning protection of buildings, structures and industrial infrastructure" (hereinafter - SO) and RD 34.21.122-87 "Guidelines for making the lightning protection of buildings and structures" (hereinafter - RD).
2. The object is classified as per the lightning protection category III. The system reliability shall be at least 0.9.
3. The object lightning protection is made by using 2-meter lightning masts installed on the roofing crests (GL-11521SS).
4. The conductors are laid by using clamp GL-11564A on the crest and GL-11747A on horizontal surfaces. The clamp spacing is 0.8 to 1.0 m. The air terminals are connected to each other by the roofing perimeter.
5. Universal clamp GL-11551A is used for securing rolled metal along the distance, as well as in the grid nodes.
6. All metal elements located on the roofing shall be connected to the lightning protection grid by using clamps GL-11545A. Stairs and handrails are connected by using clamp GL-11514.
7. Copper-plated 3-meter steel electrodes are installed as the vertical ground terminals in the embedment locations (in the corners of the object). Horizontal ground terminal represents a copper-plated steel strip with the cross-section of 30x4mm gathering all vertical electrodes into the same circuit. The distance to the object foundation is at least 1 m. The strip embedment is 0.5 to 0.7 m.
8. The ground terminal connection is made by using clamps ZZ-005-064.
9. If any ground terminal has already been installed, these shall be joined together in accordance with EIC c.1.7.55.
Intensity of lightning discharge into the ground is 6 strikes/square km/year;
Total number of strikes into the system is 0.054 (times per 19 years);
Total number of blowouts is 0.0033 (times per 303 years);
The system reliability is 0.94;
Probability of blowout into all objects of the system is 0.060.
Ground terminal resistance calculation:
Ом - Ω
м - m
Rверт - Rvert.
Rгор - Rhorizont.
The ground terminal design resistance is 10.41 Ω.
Figure 2 shows hardware layout.
Table 1 includes the list of required hardware and materials.
Заземлено и защищено - Earthed and protected
Условные обозначения - Reference designation
Молниеприёмник - мачта коньковый, высотой 2 м - Lightning mast, crest, height of 2m
Электрод D=14 мм, L=3 м - Electrode D = 14mm, L = 3m.
Полоса омеднённая стальная сечением 30x4 мм - Copper-plated steel strip, cross-section of 30x4mm
Проволока омеднённая стальная диаметром 8 мм - Copper-plated steel wire, diameter of 8mm
Опуск токоотвода - Conductor embedment
Figure 2 - Earthing and lightning protection hardware layout in the medical care dialysis center.
Table 1 – List of hardware and materials.
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