The overall objective of the Lightning Protection Assessment Study is to check and ensure that the entire plant area including structures/buildings and tank farms are safe from the lightning phenomena. The Study is carried out based on Lightning Protection Standard OISD-GDN-180 & IEC 62305.

METHODOLOGY ADOPTED

A lightning strike is an electrical discharge between the cloud and the earth. It is a natural, unpredictable phenomenon having an independent current source. The lightning has number of components such as lightning current, very high peak current, charges and a specific energy with a wave shape of 10/350 μs.

Lightning is a naturally occurring phenomenon that often causes severe damage to life and property. Direct hits may cause structural failure, whereas indirect hits through inductive or capacitive coupling, may affect the reliability and integrity of electrical and electronic equipment within the structure.

Conventional method of lightning protection system consists of lightning masts / rods exposed and placed at the highest levels of structures and connected through downward conductors to a grounding system. A design method is normally used to identify the most suitable locations for the lightning masts / rods, based on the area of protection offered by each one.

There are different methods of lightning protection systems. Examples of existing methods include geometrical constructions, such as the “Protective Angle Method” and “Rolling Sphere Method” which is based on “Electro geometric” models (EGMs). The rolling sphere method is a simple means of identifying areas of a structure that need protection, considering the possibility of side strikes to the structure. There are different radii of the rolling sphere that correspond to the relevant class of LPS. This method is suitable for defining zones of protection for all types of structures, particularly those of complex geometry. Rolling Sphere Method recognizes that the attractive effect of the lightning mast / rod is a function of a striking distance which is determined by amplitude of lightning current. This method is considered relatively simple and easy to apply.

• The protective angle method is a mathematical simplification of the rolling sphere method. The protective angle (α) is the angle created between the tip of the vertical mast / rod and a line projected down to the surface on which the rod sits.
• The protective angle differs with varying height of the air mast / rod and class of LPS. The protective angle afforded by an air rod is determined from Table 2 of IEC 62305-3.
• The protective angle method is better suited for simple shaped buildings. However, this method is only valid up to a height equal to the rolling sphere radius of the appropriate LPL.
• The rolling sphere method (RSM) is more versatile and can be used in all circumstances. Hence, the rolling sphere method is adopted for the assessing lightning protection in the plant area where numbers of lightning rods are installed in the chimneys and structures.

Lightning Risk Assessment

The assessment is based on the definitions in IEC62305-2. The result of the assessment defines the level of LPS required.

The first stage of the risk assessment is to identify which of the four types of loss (as identified in IEC 62305-1), the structure and its contents can incur. The aim of the risk assessment is to quantify and if necessary, reduce the relevant primary risks viz.

• R1- risk of loss of human life (including permanent injury)
• R2 - risk of loss of service to the public
• R3 - risk of loss of cultural heritage
• R4 - risk of loss of economic value.

R4 is considered for representative purpose only in accordance with Table 4 of IEC 62305-2: 2010. For each of the first three primary risks, a tolerable risk (RT) is set. This data can be sourced in Table 7 of IEC 62305-2.

All the major structures / buildings in the TCL plant have been evaluated for risk assessment using the flowchart.

Risk Assessment from the tank farm Area.

When producing, processing, storing, and transporting flammable substances (e.g., fuel, alcohol, liquid gas, explosive dusts) in chemical and petrochemical industrial plants, potentially explosive atmospheres often come into being in which it is imperative to avoid all sources of ignition which may cause an explosion. The relevant safety regulations describe the risk for such plants posed by atmospheric discharges (lightning strikes). In this context, it is important to note that there is a risk of fire and explosion resulting from direct or indirect lightning discharge since in some cases these plants are widely distributed. To ensure the required plant availability and safety, a conceptual procedure is required to protect parts of electrical and electronic installations of process plants from lightning currents and surges

Our Experience