Need of Lightning Risk Assessment Study
A proper lightning protection system is a must in a cement manufacturing plant as the impact of lightning strike may lead to infrastructure damage, loss of life and the disruption of plant operation.
Cement manufacturing plants are among the largest industrial plants in terms of land, equipment, buildings/structures and manpower. Operational and maintenance safety are often the regular part of this industry for uninterrupted plant operation. Safety of buildings and structures too, is always considered during the design stage taking various factors e.g. wind load, seismic zone, soil bearing capacity, etc. Among all this, one critical factor - protection system against the lightning strikes - has equal importance as that of any other safety system.
Lightning is a phenomena that cannot be prevented and the consequences need no explanation. Lightning strikes are very common in India during heavy monsoon rains. The monsoon season typically begins in June and lasts until September. However, some particular regions usually see increased lightning activity before the monsoon begins and even when monsoon goes away. In India, lightning strikes are responsible for at least 10 per cent of the total deaths caused by nature in most years and, according to the National Crime Records Bureau data, at least 2,000 deaths were associated with lightning every year since 2005.
One can still recall the incident of Korba Chimney collapse in 2009. The incident happened at an under construction thermal power plant by BALCO, during extreme weather conditions involving lightning and torrential rainfall. Workers sought shelter from the rain in a nearby store room, and a lightning strike at approximately 4.00 pm brought the chimney down.
These incidents and figures emphasises the need of a well-designed lightning protection system for such process plants including cement manufacturing plants. A proper lightning protection system (LPS) is a must as the impact of lightning strike may lead to infrastructure damage, loss of life and the disruption of plant operation. By taking a systematic approach, applying the suitable standard, carrying out a risk assessment and acting upon the results of that risk assessment, solutions can be found which are cost effective and successful.
Air terminals:The small, vertical protrusions designed to act as the 'terminal' for a lightning discharge. These terminals can be found in different shapes, sizes and designs. Most are topped with a tall, pointed needle or a smooth, polished sphere. Air termination systems can be composed of any combination of three elements, i.e. rods, catenary wires and meshed conductors.
Down conductors: Heavy cables that carry lightning current from the air terminals/rods to the ground. Cables are run along the tops and around the edges of roofs, then down one or more corners of a building to the ground rod(s). Ground terminations: Long, thick, heavy rods buried deep into the earth around a protected structure. The conductor cables are connected to these rods to complete a safe path for a lightning discharge around a structure. Surge Protection: Surge protection is the part of internal protection system and requires for the safety of electronic equipment like DCS/remote field instruments/VFDs etc.
Generally, LPS is designed and installed at many of the cement manufacturing plants during the initial stage of project itself. However, at this time, where global warming has been causing significant changes to the environment, it becomes utmost necessary to conduct the assessment of existing lightning protection systems at these plants. Lightning effects are on the rise all over the world due to changes in global weather patterns, with some climate change researchers predicting as high as a 6 per cent increase in lightning strikes for every degree of global temperature change.
Lightning Risk Assessment Study is actually the measure of risk of a lightning strike and probability of damages along with review of existing LPS. It assesses the lightening risks to the facility according to national and international standards requirements.
The method used for risk assessment study should be based on IEC 62305. The scope of IEC 62305, is to provide a procedure for the evaluation of such a risk. Once an upper tolerable limit for the risk has been ascertained, this procedure allows the selection of appropriate protection measures, in order to reduce the risk at or below the tolerable limit. To start with the study, plant layout of existing manufacturing facility, dimensional drawings of existing buildings, earth pit layout, list of field equipment for surge protection and details of existing LPS are generally required.
Risk Assessment calculations are carried out considering the standards and codes as shown in Figure-4 but not limited to. Although OISD 180 is Oil Industry Safety Directorate specifically for Lightning Protection Guidelines for Hydrocarbon Storage, sometimes is referred for oil storages in the cement plants. Factors like structure dimensions for collection area calculation, Structure attribute calculations, environmental influences, adjacent structure contribution factor derivation, power line factors, existing protection, measure, loss of human life parameter derivation etc. as per international code IEC-62305 are applied to the calculation. It is followed by the selection of areas/buildings/structures/process areas with higher probability of damages due to lightning. Based on the resultants, existing Lightning Protection Systems are compared and reviewed followed by the selection of method for external protection system.
Four classes of LPS are described as per IEC-62305 i.e LPS-I, LPS-II, LPS-III and LPS-IV wherein LPS-I being with lower risk and LPS-4 with highest risk associated. As per the results of Risk Assessment Calculation, particular class is assigned to any structure/building and accordingly, protection system is designed and suggested.
With this article, author attempts to briefly define the severity of lightning strikes and the need of carrying out Risk Assessment Study at process plants to prevent damages due to the lightning. Though lightning protection is not a legal requirement till date, businesses and manufacturing plants are required to be protected from harmful effects of natural hazards, which include lightning. Author also emphasises that stringent laws should be in place to install the adequate LPS at all process plants including cement manufacturing plants.
Author: Manoj Thakur, Head of Operations and SV Iyer, Electrical Consultant, TECHCEM Consulting and Engineering Pvt Ltd.