1. Reflect on the inter-relationship of all factors involved in the principles of chemical hazard assessment techniques and with critical insight apply them in practice.
2. Critically evaluate chemical risk information from work-based projects and with critical insight recommend justified control measures .Brief:
Local exhaust ventilation system is an engineering concept which is used in various workplaces for protecting the employees the hazardous material. For an efficient use of ventilation system, it is necessary that the system is designed & installed properly. During the welding joints of metal, intense heat is produced & high amount of electrode is consumed by the welding machine which produces welding fume. It is a mixture of gasses, metal & other hazardous compounds which is not good for health. The welding place consists of very ultra-fine particles which give irritation to eyes. For preventing this various safety measures were taken. For examples, local exhaust ventilation system & respiratory wears were the perfect examples of safety measures.
The International Agency for Research on Cancer (IARC) reported that inhalation of welding fumes enhances the probability of Cancer by 13 times then the fresh environment. It all can be minimized by local exhaust ventilation system.
Whenever we considers control, there is a standard approach. Can this step will change this present condition or all the hazardous chemical agents will be eliminated after using this method. Is the step we are taking is effective or not? So these are the various things which should be keep in mind before taking some safety measures. Installation of any control measures can be very expensive. Before installing an LEV system we should keep in our mind, there is a need of it or not. Once the LEV is installed, then its performance should be checked regularly. So that workers would get the effective environment to work.
It is the simple engineering concept of the exhaust system. It protects employees from hazard gasses. It is the only better option which removes dust & highly infected fumes from the workplace. Effective design is necessary for good health of workers. Failure of the system can lead to improper function of the design flow. The Poor designing system can lead to the leakage the work place. Employees should be properly trained so that it is easy to maintain the system.
Mainly five elements are there in this they are as follows
- Hood: it is also known as enclosure area. Contaminants are captured in this area.
- Ducting: this conducts air, which takes the contaminant particles from the hood.
- Filter: it is also known as an air cleaner.it is the system in which most of the particles are eliminated at this stage. Its essential function is to clean the air.
- Air mover: it is a system by which fan extracts power.
- Exhaust or discharge: it helps the extracted air to release at a safe place.
Design requirement for local exhaust ventilation system.
- Flow rate: flow rate is an essential factor in LEV. It consists of small contaminant particles. It carries dust particles, welding fumes, combustible substances, etc. if these all things are not extracted, then there is a risk of fire explosion. Flammable solvents are also trapped in this system. To prevent this flow rate can be increased to avoid this.
- Leak-proof: leakage in the suction pipe can create the negative pressure. Due to leakage of air, there is not much sufficient pressure in the pipe. Much pressure can be built if there is no leakage.
- For avoiding eddy current ducting need to be structured. For efficient ducting there should not be any bands or any right angle turns.
- The material of construction should be compatible so, that containments should be easily extracted we can take the example of a flammable gas system should not be generated ignition problem.
What is local exhaust ventilation (lev)?
Hood includes some times of enclosures as listed below
- Biological safety cabinet
- Ventilated Hooper
- Pouring Station
- Movable hood
- Abrasive blasting & steel cabinets
- Paint spray booth
- Portable hood with fitters
Basically, there are three types of hoods
Working position is the important factor in designing a local exhaust ventilation. If we are standing upright the exhaust pipe, then it is a wrong position to work we have to stand side by the working substance. This hood must be placed below the exhaust pipe so that exhaust gasses be blown out should not inhale by the worker at the time of operation.
Hood indicator: It is an indicator by which we can see that the system is performing correctly or not. Biological standards and safety cabinets can also be visible as an indicator.
DUCT: hood is connected with the duct. The duct is a kind of the pipeline system by which air passes to outlet frequently. Depending on the complexity of the system pipeline should not be at right angles. With this proper flow of exhaust gasses can be obtained properly. For effective use of ducting the thickness of ducting pipe should be greater so that there will not be any resistance.
Our main purpose in ducting to achieve the laminar flow of air. For achieving the laminar flow, there should not be any internal leakage.
The emission from welding & grinding is very dangerous for the workers working in the welding factory. Various types of emissions were produced by welding & grinding. Fumes of welding & grinding contain a large amount of manganese, fluorine compounds, cobalt, copper, carbon monoxide, etc. these are the various gasses which involved in the emission of welding & grinding. Fumes of gasses produced due to chemical reaction, base material, air contaminants, coatings of paint, etc.
This type of emission can adversely affect the health of workers working in welding factory. Exposure to welding fumes can make long term health effects. For avoiding the exposure of fumes local exhaust ventilation system has been installed in the company. After installing this system, it is observed that amount of emission from welding & grinding is reduced up to a great extent. It can be easily seen in below graph that how much amount of manganese is decreased with the help of local exhaust ventilation system.
So from above graph, it is clear that amount of manganese in the air is reduced from 7.23 to .091 which is a great success. So it is proved that installation of this system is very helpful the workers working the factory.
Elements of LEV system
Air filtering is the system by which contaminated air is filtered by the filters used in LEV systems. Air filter system depends on the type of air contaminants are carried out through the duct. Multi- component system has been installed in this for multiple dust particles. For example, if the size of dust are up to 30 microns, then it is separated by the major filter if the fume particles is above 40 microns then it is separated by the filters. Without causing any exposure, it should be cleaned & regularly changed.
The air mover is a fan by which exhaust gasses are blown out. It will need to provide sufficient flow rate. It creates the sufficient duct velocity so that all the contaminant particles throughout from ducts. Air mover fan should not provide a source of ignition. There are mainly three types of fan are commonly used for power extraction
- Centrifugal: A fan is used in LEV system. It creates large pressure difference so that dusted fumes can be discharged out.
- Propeller: it is used for general ventilation. It is not suitable for high-pressure resistance.
- Axial: it is not suitable for dust & fumes or small particles.
Discharge system should be placed so that it does not affect any air supply system. Air being exhausted should not be recirculated into the workplace.
An LEV System contains inlet, enclosure & hood.
There are various types of hoods. Which only depend on our requirement. Some of them are as follows receiving hood, partial enclosure, and spray painting hood.
Study population: it is a method by which it can be calculated that LEV weather system is sufficient for workers or not. An example is taken of a welding factory in which various measurements were taken before installing the LEV system in this welding factory such as inside temperature were noted, size of fume particles inside, amount of dust fumes, suffocation level, breathing level etc. after taking these measurements LEV system is properly installed & after this again particular measurements were taken then the results were incredible there is less suffocation level as compared to earlier, respiratory level increases, level of dust fumes decreases.
Sampling & determination of welding fume: in this method various samples of dust fumes were taken. The size of particles is in micron. The size particles are measured before LEV I installed sample is taken for 6 to 10 hour only. After this dust concentration is to be determined with the help of Hahn & Hebish method. With this step, we can calculate the concentration of dust particles. In this, the limit of deduction is three times the standard deviation of weight difference. Environmental conditions such as temperature, humidity were also considered with the help of calibration. 8 personal samples were taken of respirable welding so that it is to calculate the amount of gas inhaled by the worker during the welding time. Later it was resulted that plasma welding fumes consist of high amount of manganese fumes & carbon monoxide which harmful for breathing purposes.
Design feature of system for successful control
Statistical methods: All the calculation was done with the help of SAS software. By observation carried out earlier were inputted in SAS software which analyzes the data. In this statics cannot be computed by the common method. So these are the various method by which we can calculate the efficiency of LEV.
There are various misleading concepts regarding LEV, some of them are as follows.
- Air carrying from the duct system will be drawn from many directions unless it is controlled by the hood.
- Air flow will be reduced approximately 10% of total volume near by the neck of the hood.
- Operator body or any obstacle placed in the flow of path can generate dead areas.
- Duct Surfaces causes resistance in a path flow.
We can take the example of an air flow pattern
- Properly used LEV system will capture the source of emission & will protect the employee from exposure.
- General air volume can be reduced as it is not relied upon the dilute solution.
- If the system is not placed correctly, then the employee will face exposure in his face.
- Contaminants drew from the system disposed of safely.
- From the correct use of systematic employee must be well trained.
- It should be handled with care otherwise dust exposure can catch fire.
Local exhaust system development
An LEV system is shown above in which emission of welding fumes is carried out by the flexible duct away. We can obtain the desired result only when the hood is kept 15 to 20 cm away from the emission of the path. The average rate of manganese the air is .218 microgram/m³. When the LEV system is installed in breathing zone amount of manganese can be reduced by .130 microgram/m³. Exposure of manganese can be reduced by 63% with the use of this system.
The mobile LEV is shown below.
It is more suitable for heavy duty work such as for cutting operation, welding, etc. cloud fumes were very evident in breathing zone which is inhaled by the welder. When LEV is installed amount of manganese, decrease up to a certain level. Which is appropriate for welding workers.
A local exhaust system is an important system for small shops or field work. It is easily affording by low financial workers. It is a simple & effective design for small field’s purpose. Maintenance of the system is also low. Due to which it is very reliable in nature. It is very useful for the person who deals with electric arc welding which generates a high amount of fumes. It will also take care of the health of workers working in a factory. So with this, we can conclude that it is very reliable & efficient working system.
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