Blog #5 Local Exhaust Ventilation

Blog 5: Local Exhaust Ventilation

         Local Exhaust Ventilation or LEV is a control system used to reduce one’s exposure to Particulate Matter like dust, harmful fumes or gasses in an area. In laymen terms it takes an airborne contaminant out of the area and prevents a build-up of flammable gases or vapors

The main parts of an LEV:

         A hood of some kind, where the contaminants enter the system

         Duct, transports the contaminants to a filter/cleaner/exhaust point

         Air cleaner/filter/scrubber

         Air mover, like a fan to power the system

         Discharge, a safe point of air exhaust

-   

http://www.hsa.ie/eng/Publications_and_Forms/Publications/Occupational_Health/Local_Exhaust_Ventilation_LEV_Guidance.pdf

“There are two types of mechanical ventilation systems used in industrial settings: Dilution (or general) ventilation reduces the concentration of the contaminant by mixing the contaminated air with clean, uncontaminated air.

Local exhaust ventilation captures contaminates at or very near the source and exhausts them outside.”

-              -  http://www.ccohs.ca/oshanswers/prevention/ventilation/introduction.html

         A dilution ventilation does not completely remove contaminants. Should not be used for highly toxic chemical, since it’s not effective for dusts or metal fumes or large amounts of gases or vapors. It also needs large amounts of makeup air to be heated or cooled to be considered efficient. Finally it is not effective for handling a surge of gas, vapor or irregular emissions.

         Normal fans are usually ineffective as they typically blow the contaminant around the work area without effectively removing it from the immediate area. Opening a door or windows can be used as a form of dilution ventilation, however this is not reliable because the air movement is not controlled.

         A Local exhaust system traps particulate matter near the source. It is generally much more effective in controlling the flow of particulate matter. Generally, local exhaust system operates similar to a vacuum cleaner. This type of system is preferred control method when:

         The particulate matter being emitted can pose serious health risk.

         Large amounts of particulate matter is being generated.

         There is an increased heating costs from ventilation in cold weather.

         The emission sources are near a person’s breathing zones.

The limitations of an LEV system include but are not limited to:

The LEV systems will deteriorate over because of particulate matter build-up within the LEV system, especially in the filters.

LEV systems need ongoing maintenance.

There must be regular testing to ensure the system is working and effective.

Blog #4 Particulate Matter as a Health Hazards

Blog 4: Particulate matter as a health hazard

           “Particulate matter, also known as particle pollution or PM, is a complex mixture of extremely small particles and liquid droplets. Particle pollution is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles.”

-    http://www.epa.gov/oar/particlepollution/

           Particles come in many shapes and sizes, however there is a correlation between the size of particulate matter and the severity of possible health problems. Particulate matter can be grouped by size.  Bigger particles are called PM10 because they have a diameter of 2.5 and 10 micrometers. A good comparison to understand just these sizes a PM10 can be from about twenty five to a hundred times thinner than a single human hair. Smaller particles are called PM2.5 because their diameter is smaller than 2.5 micrometers. This is a hundred times thinner than a human hair.

Sources of particulate matter include,

      From Nature:

           “Dust

             Soil

             Sea salt

             Forest fire smoke

             Pollen, spores, mold

             Livestock"

Sources from Human Activities:

          “Cars

           Buses

           Boats

           Airplanes

           Construction 

           Equipment

           Lawn mowers/snow blowers

           Heating furnaces

           Factories

           Incinerators

           Power plants

           Mining

           Tobacco smoke

           Cooking smoke”

-    http://www.health.state.mn.us/divs/eh/air/pmtable1.htm

           The EPA divides Particulate Matter into two groups. Coarse particles are larger than 2.5 micrometers and smaller than ten micrometers in diameter. They can come in the shape of dirt, dust, smoke, pollen mold and spores. Fine particles, are 2.5 micrometers and smaller in diameter. These particles may be toxic organic compounds, heavy metals emitted from fire, power plants and cars.

Fine particles can be very dangerous, because their small size allows for a deeper journey into the body, the lungs or even the bloodstream. 

           

           Other factors that can affect how deep into the body particle matter goes includes, the way you breathe, fitness level, age, existing conditions and even the temperature.

Breathing through the mouth allows particulate matter to travel deeper into the body.

While exercising, particulate matter can travel deeper.

Older people breathe less deeply so particles may not get as deep.

If a lung disease blocks the airway, particles will not travel very deeply.

Depending on the weather and temperature particulate matter particulate matter can enter the body very easily and very deeply.

           All this can detrimentally affecting one’s health and hearth. These particles have been linked to severe asthma, heart attacks, premature death in people with lung or hearth disease, and severe respiratory problems like difficult breathing, coughing or intense irritation of the airways.

           Finally particulate matter can, “--be carried over long distances by wind and then settle on ground or water.  The effects of this settling include: making lakes and streams acidic; changing the nutrient balance in coastal waters and large river basins; depleting the nutrients in soil; damaging sensitive forests and farm crops; and affecting the diversity of ecosystems.”

-    http://www.epa.gov/oar/particlepollution/health.html

          Personally I think its scary just how dangerous particulate matter can be for our bodies and our ecosystem.

Blog #3 Wheatstone Bridge & Sampling

Blog 3: What is a Wheatstone bridge and how is it used for sampling?

Originally developed by Charles Wheatstone, The Wheatstone Bridge is an electrical circuit usually found in many ‘direct-reading’ instruments used to search for combustible gas. It can be used to calculate an unknown resistance by using its bridge circuit. So, two legs of the circuit are kept balanced and another used to represent the unknown resistance. It then measures the resistance and compares it to a known resistor value. Today the Wheatstone bridge is still be used to measure very low values of resistances down in the milli-Ohms range.

 -    http://www.circuitstoday.com/wheatstone-bridge-circuit

 -    http://www.electronics-tutorials.ws/blog/wheatstone-bridge.html

    Combustible gases like carbon monoxide can be detected using a sensor device with the Wheatstone bridge circuit. A catalytic sensor for example, has a filament that is coated with a catalyst. This catalyst then reacts to a combustible gas and generates heat. The change in electrical resistance of the heated filament causes an imbalance in the circuit which is recorded. 

    The readout of the device if combustible gas is found presents the concentration as in imbalance within the circuit that is proportional to the amount of combustible gas present and is expressed as a percentage. Another sensor used in combustible gas meters, also uses the measurement of thermal conductivity. Thermal conductivity is the ability of the tested air to conduct heat. Just like the catalytic combustion sensor, this sensor has a filament that is a part of the Wheatstone bridge circuit.

    Combustible gases like methane are shown as a percent of the lower explosive limit/level (LEL) also known as the lower flammable limit (LFL). Usually gas-air mixtures that encourage combustion will only do so with a certain range of concentration, with its own upper and lower limits. The LEL is the lowest gas-air mixture capable of allowing combustion to occur. Thus there is also The UEL (the upper limit of combustibility) also known as the UFL (the upper flammable limit).

Blog #2 Particle size, occupational disease & respiratory system

How particle size is related to occupational disease and respiratory system

A quick crash course on the respiratory system

The human respiratory system is a group of organs whose main function is taking in oxygen and expelling carbon dioxide. The lungs exchange these gases as we breathe. Red blood cells take oxygen from the lungs and carry it throughout the body.

During this process, red blood cells collect carbon dioxide and transport it back to the lungs, that carbon dioxide leaves the body when we exhale. When there is a decrease in oxygen its knows as hypoxia and no oxygen in the body is known as anoxia; after about four minutes without oxygen, brain cells begin to die, which can lead to brain damage and ultimately death. 

Particle Size

In industrial hygiene, particulate matter is defined as small which is less than 100 micrometers in diameter, pieces of solid materials, liquid droplets, or microbiological organisms. Since Particles smaller than about 0.001 µm start to act like gases and they are not particulate matter.

The five primary mechanisms of particle deposition are inertial impaction, interception, sedimentation, electrostatic attraction, diffusion. Because long, narrow asbestos fibers can travel through the lung and penetrate much deeper a non-fibrous particle with a diameter equal to the length of the fiber. This can result in scarring of the lungs and cancer.

 “Whether or not an airborne particle is inhaled depends on its aerodynamic diameter, the velocity of the surrounding air, and the persons’ breathing rate. How particles then proceed through the respiratory tract to the different regions of the lungs, and where they are likely to deposit, depend on the particle aerodynamic diameter, the airway dimensions and the breathing pattern.”

-     http://www.who.int/occupational_health/publications/airdust/en/

Large particles greater than > 0.5μM are usually inhaled through Impaction and Sedimentation. “Sedimentation is settlement by gravity and tends to occur in larger airways. Inertial impaction occurs when an airstream changes direction especially in the nose but also in other large airways.”

“Interception applies mainly to irregular particles such as asbestos or other fibrous dusts which by virtue of their shape can avoid sedimentation and inertial impaction. However they are intercepted by collision with walls of bronchioles especially at bifurcations or if the fibers are curved.”

Small particles less than > 0.5μM are usually inhaled through Diffusion. “Diffusion is the behavior of very small aerosol particles which are randomly bombarded by the molecules of air. It significantly influences deposition beyond the terminal bronchioles.”

-    http://www.agius.com/hew/resource/lung.htm

Effects

Pneumoconiosis is the accumulation of dust in the lungs and the tissue reaction to its presence. Two types of pneumoconiosis are coal workers pneumoconiosis and silicosis.

Silicosis is caused by pronged exposure to silica dust can be,

-    Classic Silicosis

-    Accelerated Silicosis

-    Acute Silicosis

Occupations at risk include,

-    Sandblasting

-    Miners – including coal miners

-    Quarry workers

-    Millers

-    Pottery Workers

-    Foundry

Asbestosis

-     Pulmonary Fibrosis caused by Asbestos exposure

Seen to cause:

-    Lung Cancer

-    Pleural Disease

-    Pleural Plaques

-    Diffuse pleural thickening

-    Pleural effusion

-    Rounded atelectasis

-    Malignant Mesothelioma

Inhalation Fever

      

Metal fume fever

-    Caused by metal fumes (Zinc Oxide, Copper, Magnesium, Aluminum etc.)

Organic Toxic Dust Syndrome

-    Caused by contaminated vegetables, moldy hay, compost, wood.

Pontiac Fever

-    Caused by water sources with legionella

Humidifier Fever

-    Caused by humidifiers/AC units

 Mill/Grain Fever  

-    Caused by Plant/Grain dust with endotoxins

Other diseases of the respiratory system include asthma, bronchial cancer, chronic beryllium disease and chronic bronchitis.

Introduction

Favour Ogundare

03/12/2015

OHS 2000 

ogundarespring2015ohs2000.blogspot.com