ELECTRICAL SAFETY

ELECTRICAL SAFETY

INTRODUCTION TO ELECTRICITY

Electricity is a relatively safe form of energy. It is a familiar and necessary part of everyday life, but electricity can kill or severely injure people and cause damage to property if not used sensibly. An electric shock occurs upon the contact of a (human) body part with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to describe an injurious exposure to electricity- a pathophysiological effect of an electric current through the human body. Very small currents can be imperceptible. Larger current passing through the body may make it impossible for a shock victim to let go of an energized object. Still larger currents can cause fibrillation of the heart and damage to tissues. Death caused by an electric shock is called electrocution.

The risk of electric shock is greater in certain working conditions, for example wet areas. Accidents frequently involve the use of electrical appliances and tools, and unauthorized work on the electrical equipment of machinery and fixed electrical installations. The risks can be reduced by protective measures in accordance with the relevant regulations and standards.

ELECTRICAL HAZARDS

Places of work generally have power nominally supplied at 230 volt (single phase) and 400 volt (3 phase) although some larger workplaces will receive electricity at a higher supply voltage. Working with electricity can be dangerous. Engineers, electricians, and other workers deal with electricity directly, including working on overhead lines, electrical installation and circuit assemblies. Others, such as office workers, farmers, and construction workers work with electricity indirectly and may also be exposed to electrical hazards.

· Electric Shock - The severity of an electric shock is directly related to the amount of current that passes through the body and the time it takes to pass. Lower levels may cause no more than an unpleasant tingle though it may be sufficient to cause a worker to fall from a ladder or scaffold. At medium levels it causes increased muscular tension so that anything in the grasp can scarcely be released. At high levels it can cause the heart muscles to contract irregularly and this is almost invariably fatal.

·   Burns - The passage of an electric current can cause burning at the point of contact. Severe burns can occur from an electric shock without actual bodily contact. Damp and / or wet conditions add greatly to the danger from electric shock.

· Explosion - These can be caused by an electrical discharge in an atmosphere where there are certain concentrations of flammable vapours or dust.

Basics of Contact with Electricity

It is the level of voltage  the body is exposed to and the resistance to flow of electrical current offered by the body that determines the impact of exposure to electricity. The following factors determine the severity of the effect electric shock has on your body:

• The level of voltage
• The amount of body resistance you have to the current flow
• The path the current takes through your body
• The  length  of  time  the  current  flows  through your body

If a worker has come into contact with electricity the worker may not be able to remove themselves from the electrical source. The human body is a good conductor of electricity. If you touch a person while they are in contact with the electrical source, the electricity will flow through your body causing electrical shock. Firstly attempt to turn off the source of the electricity (disconnect). If the electrical source can not readily and safely be turned off, use a non-conducting object, such as a fibreglass object or a wooden pole, to remove the person from the electrical source.

How Electric Current affects the Body

Electric Current affects the body when it flows through. The basic unit of current is the amp. This is the current which flows through a resistance of 1 ohm (Ω) when a voltage of 1 volt is applied across it. However, currents as low as thousandths of amps (milliamps) can have an adverse effect on the body. The table below gives an illustration of the types of effects various levels of currents can have on the body.

Electric   Current (1 second contact)	Physiological Effect
1 mA	Threshold of feeling, tingling sensation.
5 mA	Accepted as maximum harmless current
10-20 mA	Beginning of sustained muscular contraction ("Can't let go" current.)
100-300   mA	Ventricular fibrillation, fatal if continued. Respiratory function continues.
6 A	Sustained ventricular contraction followed by normal heart rhythm. (defibrillation). Temporary respiratory paralysis and possibly burns.

30 mA can cause the onset of potentially fatal respiratory paralysis. The adverse effect will be directly related to the level of current, the length of time that the body is exposed and the path the current takes through the body.

SAFETY PRECAUTIONS

Electrical exposure causes injuries in direct proportion to the amount of electricity and the time of exposure. It follows that any effort made to reduce the amount of electricity will also reduce the severity of the consequences of any exposure. Electrical equipment on building sites, particularly power tools and other portable equipment and their leads face harsh conditions and rough use. They are likely to be easily damaged and become dangerous. Modern double insulated tools are well protected but their leads are still vulnerable. Precautions which can be taken are:

• Where possible, use a 110 volt supply system which is centre-tapped to earth so that the maximum voltage to earth should not exceed 55 volts. This will effectively eliminate the chance of death and greatly reduce injury in the event of an electrical accident. Even lower voltages can be used for lighting systems to further reduce risk.
• If mains voltages must be used, then extra precautions should be taken. Trip devices such as residual current devices (RCDs) rated at 30 mA will be needed to ensure that the current is properly cut off if contact is made with any live part. Such devices must be treated with great care and kept free of moisture and dirt and should be tested daily by operating the test button. If permanent wiring is being installed as part of the works and it is to be fitted with a trip device it is a good idea to design this work to be done at the beginning of the project so that it can be used during the construction period.
• On sites where temporary mains cable is to be used this should be installed in such a way as to avoid damage. For instance, it should be slung at ceiling height. Where mains leads to sockets may be damaged they should be positioned where they are least likely to sustain such damage or protected inside non-conducting conduit. Electric bulbs should be protected and damaged bulbs replaced.
• Electrical systems should be regularly checked and maintained by a qualified electrician. In addition users of electrical tools and equipment should be trained to carry out daily checks on the condition of the cables, the plug and the general condition of the device. The RCD should also be tested daily by pressing the test button. Any defects detected should be reported immediately and the device taken out of service.
• In addition to user checks mains voltage systems should be checked and tested weekly by a competent electrician and the results of such tests should be recorded.
• Work in areas where there is a risk of flammable vapours such as petrol stations or petrol-chemical plants may require the use of specially designed equipment to prevent sources of ignition such as sparks or overheating. Such precautions should be specified in the Pre-construction Information for the Project and the advice of a specialist may be necessary.
• The electricity supplier should be informed of the nature, duration and likely start date of the work.
• The location of overhead lines and buried cables should be identified as part of the Health and Safety Plan and where possible overhead lines should be re-routed or the power switched off. It may be possible to site the structures away from them thus "planning out" the hazard.
• Where the use of very heavy plant using a high voltage supply is planned then close liaison with the electricity supplier is essential and specialist advice may be necessary.

EARTHING

What is Electrical Earthing System?

Earthing is the method of transmitting the instant electricity discharge directly to the ground through low resistance wires or electrical cables. This is one of the significant features of electrical networks. Because it builds the most eagerly accessible and hazardous power source much secure to utilize.

The process of earthing in case of short circuit condition, the electrical wire carefully removes the overflow of current and allows it to flow through the earth.

Why Earthing is Required?

The main intention of electrical earthing is to keep away from the danger of electric shock due to the outflow of current from ground through the not preferred path as well as to make sure that the potential of a conductor does not increase with respect to the ground than its planned insulation.

When the metallic element of electrical machines approaches in contact by an existing wire, due to a breakdown of fixing the cable, the metal turn into charged and static charge collect on it. If someone contacts such an electric metal, then the outcome is a severe electric shock. So finally

We can conclude that life is random, and one should always get ready for unexpected circumstances. So buildings and electric appliances have to be grounded to transfer the electric charge directly to the ground. The main benefits of grounding include protection from overvoltage, stabilization of voltage, and prevention form injury, damage, and death.

Components used in Electrical Earthing System

The main components used in earthing system mainly include earth cable, earthing joint (earthing lead), and earth plate

Earth Cable

The conductor is used to connect metallic parts of an electrical system like plug sockets, metallic shells, fuses, distribution boxes. Metallic parts of motors, transformers, generators, etc. the range of these conductors depend on the earth cable size used in the wiring circuit. The earth wire in the cross-sectional area must be less than the solid wire used in the electrical wiring system.

In general, the copper wire utilized as an earth continuity conductor size is 3-standard wire gauge (SWG). Ground wires which are smaller than 14-SWG should not be used. In some situations, copper strips are used instead of a bare copper conductor.

Earthing Joint

The ‘ground electrode’ as well as conductors fixing to the ‘ground continuity conductor’ is called earthing joint (earthing lead).  The tip where the earthing joint connects the ground continuity conductor is known as connecting end. The lead of the ground must be low size, straight, & should include a minimum amount of joints. Although copper wires are usually used as grounding leads; whereas copper strips are selected for high fitting because it carries high fault current values due to its broad region.

Earth Plate

The last part of the electrical grounding system which is hidden underground and linked to the lead of grounding is known as the earth plate. Earth electrode is a pipe, plate or metallic rod, or plate; which has extremely low resistance for carrying the fault current to the ground safely.

It can be of iron or copper rod and must be placed in wet earth and in case the moisture content of earth is low then put some water in the earth plate. The earth plate is always placed in the vertical, and coat with salt and charcoal lime around the earth plate. This helps in protecting the earth plate as well as in maintains ground moisture around the earth plate. The earth plate must be placed four meters long for the better earthing.

Types of Electrical Earthing Systems

The process of Earthing or electrical grounding can be done in several ways like wiring in factories, housing, other machines, and electrical equipment. The different types of electrical earthing systems include the following.

Plate Earthing System

In this type of system, a plate is made up of copper or GI (galvanized iron) which are placed vertically in the ground pit less than 3meters from the earth. For a better electrical grounding system, one should maintain the earth moisture condition around the plate earthing system. 

 

Pipe Earthing System

A galvanized steel based pipe is placed vertically in a wet is known as pipe earthing, and it is the most common type of earthing system. The pipe size mainly depends on the soil type and magnitude of current. Usually, for the ordinary soil, the pipe dimension should be 1.5 inches in diameter and 9feets in length. For rocky or dry soil, the pipe diameter should be greater than the ordinary soil pipe. The soil moisture will decide the pipe’s length to be placed in the earth.

Rod Earthing System

This type of earthing system is similar to pipe earthing system. A copper rod with galvanized steel pipe is placed upright in the ground physically or using a hammer. The embedded electrodes lengths in the earth decrease the resistance of earth to a preferred value.

The earthing system or electrical grounding system offers greater safety from electric shock for personal, equipment, buildings, etc. The ground sensitivity can be the earth resistivity can be affected by some issues like soil and climate, a condition of resistivity, moisture, melted salts, earth pit location, physical work, grain size effect, current magnitude, etc.

RCCB (Residual Current Circuit Breaker)

RCCB (Residual current circuit breaker) or RCD (Residual-current device) are aimed to protect people from the risk of electrocution and fire that are generally caused due to the faulty wiring. An RCCB is also very useful when a sudden earth fault occurs in the circuit.

RCCB is basically an electric wiring that trips or disconnects when imbalance or mismatch in electric current is detected. The best part about RCCB is that it does not take much time to take the control over the imbalanced electric current; RCCB takes only about 20 milliseconds to trip. RCCB is essentially a current sensing equipment that is used to control the low voltage circuit from the fault. It comprises a switch device which is used to turn off the circuit when there is a fault.

MCB (Miniature Circuit Breaker)

All fuses need to be replaced with the MCB for safety and control purposes.MCBs are electromechanical devices which are used to protect an electrical circuit from an overcurrent. It can be reclosed without any hand-operated restoration. MCB is used as an option to the fuse switch in most of the circuits. Unlike a fuse, MCB does not have to be replaced every time after a failure as it can be reused.

Another huge advantage of MCBs is that the detection of a problem is easy. Whenever there is a fault in the circuit, the switch comes down automatically and we are hereby informed that there was a fault. We can then manually go and put the MCB back up and the electricity will start flowing again.

ISOLATORS 

Circuit breaker always trips the circuit but when there is an open contact of the breaker,it cannot be physically seen from outside of the breaker and that is why it is considered as the “not to touch” area of the electrical circuit. Thus, the isolators are created for the safety so that, one can see the condition of the section of the circuit before touching it. The isolator is a switch which isolates the part of the circuit system when it is required. Electrical isolators are the separate part of the system that is created for the safe maintenance. Isolators are generally used at the end of the breaker to repair or to replace.

The main difference between MCB, RCCB, and Isolators

Isolators are generally used in power system while on the other hand, MCB is the circuit breaker. Isolators are manually-operated device, and on the contrary, the circuit breaker is the automatically-operated device. Isolators cut the portion of the substance when a fault occurs. The other devices like MCB and RCCB operate without any interruption. The circuit breaker is the device of an Automatic circuit breaker or Miniature circuit breaker which trips the entire system and if any fault occurs, MCB is to protect the wires from the damage. Whereas, on the other hand, residual current device protects the life-threatening problems. RCCB detects the leakage current and protects from the electric shock.

FIRST AID MEASURES

1. Quickly assess the situation.
2. Cut the power and move the injured person without endangering yourself.

• Cut the power by using a switch, removing a fuse or in a similar manner.
• If the power cannot be cut quickly, move the injured person away from the source of electricity with an insulating object, such as a dry piece of wood, rope or clothing.
• Never use moist or metallic objects for moving the injured person.
• In high-voltage accidents, you should not start actual rescue measures before a professional electrician has cut the power.

3. Check the condition of the injured person.

• When a person suddenly loses consciousness or appears lifeless, immediately check if he/she can be woken up by speaking to or shaking the person.

4. Call for an ambulance

• If the injured person will not wake up and is unresponsive, call for help and ask one of the people present to call for an ambulance. If you are alone, make the call yourself. Follow the instructions given by the emergency response centre.

5. Give first aid.

• Open the airways and check for breathing: Lift the chin upwards with two fingers and tilt the head back with your other hand by pressing on the forehead. See if the chest is moving, and if you can hear normal sounds of breathing or feel an air stream on your cheek.
• If the person is breathing normally place the person on his/her side to secure breathing. Monitor the breathing until professional help arrives.
• If breathing is not normal, start chest compressions. Place the palm of your hand in the centre of the sternum and your other hand on top of it. Give 30 compressions with straight arms in a piston-like motion with the speed of approximately 100 compressions per minute. Let the chest compress roughly 4 – 5 cm.
• Continue with mouth-to-mouth resuscitation. Open the airways again. Lift the chin upwards with two fingers and tilt the head back with your other hand by pressing on the forehead. Close the nostrils with your thumb and index finger. Seal your lips tightly around the person’s mouth and blow air into the lungs 2 time while monitoring the movement of the chest.
• Continue CPR with the rhythm of 30 compression and 2 blows, until you can hand the responsibility over to professionals, breathing returns or you become to tired to continue.

CHECKLIST FOR BASIC ELECTRICAL SAFETY

Inspect Cords and Plugs

• Check extension cords and plugs daily. Do not use, and discard corns and plugs if they are worn or damaged.
• Have any extension cord that feels more than comfortably warm checked by an electrician.

Eliminate Octopus Connections

• Do not plug several items into one outlet.
• Pull the plug, not the cord.
• Do not disconnect power supply by pulling or jerking the cord from the outlet. Pulling the cord causes wear and may cause a shock.

Never Break OFF the Third Prong on a Plug

• Replace broken 3-prong plugs and make sure the third prong is properly grounded.

Never Use Extension Cords as Permanent Wiring

• Use extension cords only to temporarily supply power to an area that does not have a power outlet.
• Keep extension cords away from heat, water and oil. They can damage the insulation and cause a shock.
• Do not allow vehicles to pass over unprotected extension cords. Extension cords should be put in protective wireway, conduit, pipe or protected by placing planks alongside them.

ELECTRICAL SAFETY TIPS

•  Inspect portable cord-and-plug connected equipment, extension cords, power bars, and electrical fittings for damage or wear before each use. Repair or replace damaged equipment immediately.
• Always tape extension cords to walls or floors when necessary. Do not use nails and staples because they can damage extension cords and cause fire and shocks.
• Use extension cords or equipment that is rated for the level of amperage or wattage that you are using.
• Always use the correct size fuse. Replacing a fuse with one of a larger size can cause excessive currents in the wiring and possibly start a fire.
• Be aware that unusually warm or hot outlets or cords may be a sign that unsafe wiring conditions exists. Unplug any cords or extension cords from these outlets and do not use until a qualified electrician has checked the wiring.
• Always use ladders made with non-conductive side rails (e.g., fibreglass) when working with or near electricity or power lines.
• Place halogen lights away from combustible materials such as cloths or curtains. Halogen lamps can become very hot and may be a fire hazard.
• Risk of electric shock is greater in areas that are wet or damp. Install Ground Fault Circuit Interrupters (GFCIs) as they will interrupt the electrical circuit before a current sufficient to cause death or serious injury occurs.
• Use a portable in-line Ground Fault Circuit Interrupter (GFCI) if you are not certain that the receptacle you are plugging your extension cord into is GFCI protected.
• Make sure that exposed receptacle boxes are made of non-conductive materials.
• Know where the panel and circuit breakers are located in case of an emergency.
• Label all circuit breakers and fuse boxes clearly. Each switch should be positively identified as to which outlet or appliance it is for.
• Do not use outlets or cords that have exposed wiring.
• Do not use portable cord-and-plug connected power tools if the guards are removed.
• Do not block access to panels and circuit breakers or fuse boxes.
• Do not touch a person or electrical apparatus in the event of an electrical incident. Always disconnect the power source first.

TIPS FOR WORKING WITH POWER TOOLS

• Switch all tools OFF before connecting them to a power supply.
• Disconnect and lockout the power supply before completing any maintenance work tasks or making adjustments.
• Ensure tools are properly grounded or double-insulated. The grounded equipment must have an approved 3-wire cord with a 3-prong plug. This plug should be plugged in a properly grounded 3-pole outlet.
• Test all tools for effective grounding with a continuity tester or a Ground Fault Circuit Interrupter (GFCI) before use.
• Do not bypass the on/off switch and operate the tools by connecting and disconnecting the power cord.
• Do not use electrical equipment in wet conditions or damp locations unless the equipment is connected to a GFCI.
• Do not clean tools with flammable or toxic solvents.
• Do not operate tools in an area containing explosive vapours or gases, unless they are intrinsically safe and only if you follow the manufacturer's guidelines. 

TIPS FOR WORKING WITH POWER CORDS

• Keep power cords clear of tools during use
• Suspend extension cords temporarily during use over aisles or work areas to eliminate stumbling or tripping hazards.
• Replace open front plugs with dead front plugs. Dead front plugs are sealed and present less danger of shock or short circuit.
• Do not use light duty extension cords in a non-residential situation.
• Do not carry or lift up electrical equipment by the power cord.
• Do not tie cords in tight knots. Knots can cause short circuits and shocks. Loop the cords or use a twist lock plug.

An unrecognized hazard can never be controlled

Hazard recognition is one of the most critical aspects of occupational safety. “One of the ‘root causes’ of workplace injuries, illnesses, and incidents is the failure to identify or recognize hazards that are present, or that could have been anticipated.”

The recognition of hazards involves the study of work processes, to identify possible factors which may pose health and safety hazards. This is a fundamental step in the practice of occupational hygiene. Hazards which are not recognized will be neither evaluated nor controlled.

Recognition requires the basic background information. But to apply it in the workplace requires a systematic approach, consisting of gathering of information and a workplace survey, not necessarily involving measurement. However, a quantitative evaluation of the risks and of the necessary control measures may then be needed.

The steps for an adequate hazard recognition are: ·

1.  Initial collection of information on the process in question and potential associated       hazards, from the literature and/or previous surveys, if any;
2.  Actual visit to the workplace for detailed observation (usually referred to as “walkthrough” survey); and, ·
3.  Subsequent analysis of the observations.

The first step is collection of information to optimize the actual observations. In order to avoid overlooking potential hazards during the walk-through survey, it is important to make a record of the observations.

Collection of information about hazards will continue during the walk-through survey. However, the walk-through survey will also review how materials are being used, what potential  hazards exists, what control measures (if any) are in place, and the degree to which these appear to be performing effectively.

Whenever hazards are evident and serious, the qualitative hazard assessment made during the recognition step, particularly the information obtained during the walk-through survey, should be enough to indicate the need for control measures, regardless of further quantitative exposure assessment. Priorities for follow-up action should be established taking into account the severity of the risk and the number of workers likely to be exposed In such cases, the walk-though survey will provide enough information to recommend immediate preventive measures, without the need for measurements.

Hazard identification and recognition is definitely an essential skill for all workers. And a person doesn’t become skillful in hazard recognition simply by knowing what hazards are. One has to get trained to become proficient at this. So, the first step of training workers for a job role is to help them learn the basic-level knowledge and skills. Then we can use scenario-based learning and other forms of training to help them develop the advanced job skills. Scenario based training can engage the workers and help them fully understand safety rules and procedures.

USING SCENARIO-BASED TRAINING FOR WORKFORCE

Scenario-based learning is a way of teaching or practicing a skill using interactive, problem-based contexts. This strategy usually involves learners working their way through a problem, which they are expected to solve. In the process, learners must apply their prior experience, subject knowledge, critical thinking, and problem solving skills in a risk-free and “close-to real-world” environment. This allows them to acquire the necessary skills needed to deal with similar problems at work.

Scenario-based learning programs are based on situations which your people face every day in their work. For example, if an employee is working in a workshop with metal objects, the scenarios provided to him would include contexts such has handling metal sheets, the right way of servicing knives and blades, etc. These scenarios help the learners immediately connect to their work and the hazards they might face.

Did you know

ILO estimates that every year over 317 million workers are involved in non-fatal occupational accidents causing serious injuries and absences from work.

Biogeochemical Cycles / Nutrient Cycles

Biogeochemical cycles / Nutrient cycles

The cycling of chemicals between the biological and the geological world is called Biogeochemical cycle.

The Biotic and Abiotic components of the biosphere constantly interact through biogeochemical cycles. During these interactions, there is a transfer of nutrients between living organisms and the non-living environment.

The  important biogeochemical cycles are water cycle, Nitrogen cycle, Carbon cycle and Oxygen cycle, Phosphorus cycle and Sulphur cycle.

Biogeochemical Cycles are classified into :

1. Atmospheric cycles - Ex: Carbon, Oxygen and Nitrogen cycles
2. Hydrological cycle  - Ex: Water cycle
3. Sedimentary cycle   - Ex: Phosphorus and Sulphur cycles

Water cycle

The water cycle involves various steps like evaporation, transpiration, condensation and precipitation.

    •  When the water bodies are heated during the day, water enters the atmosphere as water vapour by the process of evaporation.

    •  There is another way in which water evaporates into the atmosphere. This happens through transpiration.

    •  The water vapours in the atmosphere changes to water droplets and collects to form clouds. This process is called condensation.

    •  Air currents move the clouds formed by condensation and carry them over the land, where they break into rain, snow or fog. This is called precipitation.

Nitrogen cycle

The sequence in which nitrogen passes from the atmosphere to the soil and organisms, and then is eventually released back into the atmosphere, is called the Nitrogen cycle.

 • Nitrogen makes up 78 percent of the earth’s atmosphere. The percentage of nitrogen in the atmosphere is maintained by nitrogen cycle.

  • Nitrogen is an essential constituent of proteins, nucleic acids like DNA and RNA, vitamins, and chlorophyll.

 • Plants and animals cannot utilise atmospheric nitrogen readily. It has to be fixed by some organisms called as nitrogen fixers.

 • Nitrogen-fixing bacteria live in the root nodules of certain leguminous plants.. These bacteria convert atmospheric nitrogen into ammonia, which is utilised readily by plant called Nitrogen fixation.

  •  Nitrogen-fixing bacteria along with free living bacteria in the soil achieve 90 percent of nitrogen fixation.

 • Lightning plays an important role in nitrogen fixation. When lightning occurs, the high temperature and pressure convert nitrogen and water into nitrates and nitrites.Nitrates and nitrites dissolve in water and are readily used by aquatic plants and animals.

   • Ammonification is the process by which soil bacteria decompose dead organic matter and release ammonia into the soil.

   •  Nitrification is the process by which ammonia is converted into nitrites and nitrates.

   •  Denitrification is the process by which nitrates are converted into atmospheric nitrogen.

              

Carbon cycle

Carbon is cycled repeatedly through different forms by the various physical and biological activities constituting the carbon cycle.

Carbon cycle maintains the balance of the element carbon in the atmosphere. Carbon is found in various forms on the Earth. 

*Diamond and graphite found in the soil are made up of an element called carbon. 

*Carbon is present in the atmosphere as carbon dioxide. 

*Carbon can also occur as carbonates and bicarbonate salts in minerals. The endoskeletons and exoskeletons of various aquatic animals are also formed from carbonate salts.

*Carbon is an essential part of nutrients like carbohydrates, fats, proteins, nucleic acids and vitamins.

Carbon cycle maintains the amount of carbon in the atmosphere. The carbon cycle starts in plants. 

Step - 1 : Plants, use carbon dioxide in the atmosphere, convert it into glucose in the presence of sunlight by the process of photosynthesis. Plants and animals break these carbohydrates for energy and release carbon dioxide through respiration.
Step - 2 : When the plants and animals die, fungi and bacteria decompose the dead remains.  This releases the carbon in the remains as carbon dioxide. 
Step - 3 : Some plants and animals which get burried in the soil under certain temperature and pressure over millions of years get transformed into fossil fuels. Coal and petroleum are some of the fossil fuels. On burning these fuels, carbon dioxide is released into the atmosphere. 

                    

Oxygen cycle

The sequence in which oxygen from the atmosphere is used by organisms and eventually released back into the atmosphere through photosynthesis is called as oxygen cycle.

    •  Oxygen makes up 21 percent of the air. It is an essential constituent of carbohydrates, proteins, fats and nucleic acids. 

    •  Oxygen is found in air, in combined form as carbon dioxide, and in the earth’s crust as carbonates, sulphates and nitrates. 

    •  Plants and animals use atmospheric oxygen during respiration and release the same during photosynthesis. 

    •  Fossil fuels require oxygen for combustion. 

    •  The ozone layer is present in stratosphere, one of the layers of the atmosphere. Each molecule of ozone is made up of three oxygen atoms. The ozone layer prevents harmful radiations from reaching the earth’s surface, where they might damage life forms.

                                  
Phosphorus cycle

 Phosphorous is an essential nutrient found in the macromolecules of humans and other organisms, including DNA

·    The phosphorous cycle is slow. Most phosphorous in nature exists in the form of phosphate ion.  Phosphorus is often the limiting nutrient, or nutrient that is most scarce and thus limits growth, in aquatic ecosystems.

·     When nitrogen and phosphorous from fertilizer are carried in runoff to lakes and oceans, they can cause eutrophication, the overgrowth of algae. The algae may deplete oxygen from the water and create a dead zone.

In nature, phosphorous is found mostly in the form of phosphate ions. Phosphate compounds are found in sedimentary rocks, and as the rocks weather wear down over long time periods the phosphorous they contain slowly leaches into surface water and soils. Volcanic ash, aerosols, and mineral dust can also be significant phosphate sources.

Phosphate compounds in the soil can be taken up by plants and, from there, transferred to animals that eat the plants. When plants and animals excrete wastes or die, phosphates are returned to the soil. Phosphorous-containing compounds may also be carried in surface runoff to rivers, lakes, and oceans, where they are taken up by aquatic organisms.

When phosphorous-containing compounds from the bodies or wastes of marine organisms sink to the floor of the ocean, they form new sedimentary layers. Over long periods of time, phosphorous-containing sedimentary rock may be moved from the ocean to the land by a geological process called uplift. However, this process is very slow, and the average phosphate ion has an oceanic residence time in the ocean of 20,000 to 100,000 years.

Sulphur Cycle:

Sulphur is one of the components that make up proteins and vitamins. Proteins consist of amino acids that contain sulphur atoms. Sulphur is important for the functioning of proteins and enzymes in plants, and in animals that depend upon plants for sulphur.

It enters the atmosphere through both natural and human sources. Natural recourses can be for instance volcanic eruptions, bacterial processes, evaporation from water, or decaying organisms. When sulphur enters the atmosphere through human activity, this is mainly a consequence of industrial processes where sulphur dioxide (SO₂) and hydrogen sulphide (H₂S) gases are emitted on a wide scale.

When sulphur dioxide enters the atmosphere it will react with oxygen to produce sulphur trioxide gas (SO₃), or with other chemicals in the atmosphere, to produce sulphur salts. Sulphur dioxide may also react with water to produce sulphuric acid (H₂SO₄). Sulphuric acid may also be produced from demethyl-sulphide, which is emitted to the atmosphere by plankton species.

All these particles will settle back onto earth, or react with rain and fall back onto earth as acid deposition. The particles will then be absorbed by plants again and are released back into the atmosphere, so that the sulphur cycle will start over again.