Lecture 1 Putting Safety Into Perspective

Industrial Ventilation- A major control measure8th LecturebyMuhammad Shahbaz GulzarPPT-040-01 4Ventilation The process of "changing or replacing air in any space to provide high quality indoor air

To:Remove unpleasant smells and moistureIntroduce outside air Improve circulation, etc.

In firefighting, refers to a tactic of creating a draft to control the release of heat and smoke

Ventilating (the V in HVAC) is the process of "changing" or replacing air in any space to provide high indoor air quality (i.e. to control temperature, replenish oxygen, or remove moisture, odors, smoke, heat, dust, airborne bacteria, and carbon dioxide). Ventilation is used to remove unpleasant smells and excessive moisture, introduce outside air, to keep interior building air circulating, and to prevent stagnation of the interior air.Ventilation includes both the exchange of air to the outside as well as circulation of air within the building. It is one of the most important factors for maintaining acceptable indoor air quality in buildings. Methods for ventilating a building may be divided into mechanical/forced and natural types.[1]

In firefighting, ventilation refers to the tactic of creating a draft with an opening above or opposite the entry point so that heat and smoke will be released, permitting the firefighters to find and attack the fire. If a large fire is not properly ventilated, not only will it be much harder to fight, but it could also build up enough poorly burned smoke to create a smoke explosion, or enough heat to create a flashover. Contrarily, poorly placed or timed ventilation may increase the fire's air supply, causing it to grow and spread rapidly.Mechanical fans can be used for such ventilation tactics, as can existing openings such as windows, skylights or heat/smoke vents on the roof. If there is no suitable existing hole, firefighters may use their equipment to make one, such as specialised saws for cutting a large hole in the roof. A conical hose-stream aimed around an opening -of a window or door, etc.- entrains smoke and thus increases the exhaust rate of smoke from the space. This is a process called "hydraulic ventilation". This strategy might be used when the fire is small and protecting property from smoke damage can be achieved safely. It can also be used more aggressively when a structure is "fully involved" and the smoke is obstructing the nozzlemans view of the hotspots.High-rise buildings sometimes also incorporate fans to produce a positive pressure in stairwells and elevator shafts to reduce smoke infiltration into those spaces.When glass windows in a burning structure burst from internal pressure and heat, or the fire burns through the roof, it may be said to have "auto-ventilated" or "self-ventilated."

2The work environment.The work environment in the textile mills is dominatly harmful/ dangerarous due to noise, dust, and heat. The production uses a vast quantity of water and variety of chemicals. These generate liquid waste containing substantial pollutants in the form of organic and suspended matter, such as fibres and grease.3Risk due to exposure to dust.Chronic exposure has caused lung airway obstraction (which reduce ventilatory capacity) and lead to disability and premature death. For short term exposure (acute), exposure to cotton dust can produce a feeling of chest tightness, coughing, wheezing, phlegm, weakness, fever, chills, and breathing difficult (dyspnea). The symptoms can disappear following removal from exposure (during brief periods away from work) and can reappear following expossure.

4Operation and method of control of dust.

During carding operation, mixing and blowing operations, bale breaking, manufacturing of cotton yard, and handling of cotton seed in the extractraction of cotton seed oil, the dust is controlled through process enclosure, local exhaust ventilation (LEV), personal protective equipment.During cotton balling operations and weaving of textile containing cotton yarn, dust is controlled through general dilution and ventilation.

During raw cotton ginning, back pressing and harvesting dust is controlled through local exhaust ventilation, personal protective equipment.

5Hazards of Poor or No VentilationISTAR, SPU VVN Anand6Lack of oxygen (headache, fatigue, Asphyxiation, particularly in confined spaces)Excessive heat, cold, and humidityToxic fumes (e.g.- Lead, cadmium, zinc)Toxic vapors (e.g.- Benzene)Toxic gases (e.g.- Hydrogen Sulphide, ammonia)Dusts (causing poisoning or gradually reduced lung capacity)Fire/explosion7What Is Industrial Ventilation?Environmental engineers view: The design and application of equipment for providing the necessary conditions for maintaining the efficiency, health and safety of the workers.

Industrial hygienists view: The control of emissions and the control of exposures.

Mechanical engineers view:The control of the environment with air flow. This can be achieved by replacement of contaminated air with clean air8Why Industrial Ventilation?To maintain an adequate oxygen supply in the work area.To control hazardous concentrations of toxic materials in the air.To remove any undesirable odors from a given area.To control temperature and humidity.To remove undesirable contaminants at their source before they enter the work place air.9Types Of Industrial Ventilation Systems Supply systemsTo create a comfortable environment in the plant i.e. The HVAC systemTo replace air exhausted from the plant i.e. The replacement systemExhaust SystemsAn exhaust ventilation system removes the air and airborne contaminants from the work place airThe exhaust system may exhaust the entire work area, or it may be placed at the source to remove the contaminant at its source itself

10What is the difference between Exhaust and Supply systems?

An Exhaust ventilation system removes the air and air borne contaminants from the work place, whereas, the Supply system adds air to work room to dilute contaminants in the work place so as to lower the contaminant concentrations.

11Supply SystemsComponentsAir inlet sectionFiltersHeating and/or cooling equipmentFanDuctsRegister/grills for distributing the air within the work space12Exhaust SystemsTypes of exhaust systems:

General exhaust systemLocal exhaust system

General (dilution) ventilation systems supply clean air that mixes with the air in the workplace, diluting the concentration of the contaminant.General ventilation is not suitable to control exposure to toxic substances because these systems actually spread the contaminant throughout the workplace before exhausting it.Also, they require large amounts of air and may be costly to operate during the winter because of additional heating.General ventilation systems are used primarily to control temperature and humidity, to remove odours, and sometimes to remove traces of toxic substances and microorganisms emitted from carpeting, furniture, and people.General Exhaust Systems14General Exhaust SystemsApplicationUsed for heat control in an area by introducing large quantities of air in the area. The air may be tempered and recycled.Used for removal of contaminants generated in an area by mixing enough outdoor air with the contaminant so that the average concentration is reduced to a safe level. Two TypesNatural Ventilation: uses wind.Mechanical Ventilation: Uses fan (with or without duct)

General or Dilution Ventilation1. Natural Ventilation2. Mechanical VentilationPreferred if significant health hazards existClean Air SupplyZone of Contaminant ReleaseOperators Breathing ZoneDischarge OpeningDirection of air flow must remove contaminants from workers breathing zone

XRecommended PracticesISTAR, SPU VVN Anand171718Local Exhaust Ventilation (LEV)The objective of a local exhaust system is to remove the contaminant as it is generated at the source itself. Advantages:More effective as compared to a general exhaust system. Remove contaminant before it has a chance to spread.The smaller exhaust flow rate results in low heating costs compared to the high flow rate required for a general exhaust system.The smaller flow rates lead to lower costs for air cleaning Components:HoodThe duct system Air cleaning deviceFan, which serves as an air moving device

Local Exhaust VentilationHood or exhaust inletDuctingFilter or purifying systemFan and motorExhaust outletDucting

LOCAL EXHAUST VENTILATION SYSTEMDuctHoodsAir Cleaning DeviceFanISTAR, SPU VVN Anand21Hoods - any point where air is drawn into the ventilation system to capture or control contaminants.The hood captures the contaminant by overcoming its momentum and then drawing it into the system. For large, heavy dust particles released at high speeds (e.g., grinding), the hood must be positioned in the path of the particles.

Ducts - the network of piping that connects the hoods and other system components.The duct work provides a pathway to carry the contaminant to the air cleaning device. The velocity of air in the duct must be high enough to prevent heavy particles from settling in the ducts. The heavier the particle, the greater the velocity needed. Also, there should be no obstructions or unnecessary bends and constrictions. These can cause excessive pressure drops.

Fan - air-moving device that provides the energy to draw air and contaminants into the exhaust system & through the ducts and other components.Air Cleaner - a device to remove airborne materials that may be needed before the exhaust air is discharged into the community environment.The air cleaning device removes contaminants fromthe air stream before it is passed to the fan andexpelled to the atmosphere or recycled to the workarea. There are two types of air cleaning devices: air filters and dust collectors.Air filters are designed to remove low dust concentrations of the magnitude found in atmospheric air. Dust collectors are designed for the heavier concentrations that are generated by industrial processes.Local exhaust ventilation hoods:

Capture mobile23There are a large range of different types and designs of LEV hood and there appears to be no common design principles.The new HSE guidance (HSG 258) states that there are only three types of LEV hood.

Capturing (Capture)The three basic types of LEV hoodEnclosing (Contain and separate)Receiving (Receive, contain & empty)

24Enclosures process takes place inside the hood. The hood needs to contain the airborne contaminant and keep it separate from the worker

Receptor process takes place outside of the hood, but the process generates directional air movement towards the hood. The hood needs to receive the contaminated laden air and to ensure it works effectively it needs to empty at lease as quick as it is being filled.

Capturing process takes place outside the hood. The hood has to generate sufficient air movement towards the hood at the far side of the source. Effectively, the hood has to reach out and capture the contaminant laden air.

Most LEV hoods fall into one of the above categories, but sometimes hoods do operate in mixed modePartial, largeRoomLEV hood classification expanded Receiving

Capturing

HotPartial, smallFullEnclosures

25Hemeon refers to three different types of hood; exterior (which is equivalent to capturing), enclosing and Canopy or receiving hoodEnclosures Can be subdivide - full, partial (large), partial (small), room

Receiving Process moves in one direction. classic receiving hood is the canopy hood above a hot process

In practice the guidance will use the classification to outline key design factors for each type of hood and common errors but also will refer to and use the more familiar terms where appropriate e.g. enclosure, partial enclosure and canopy hoodCapturing Hoods

Hood has to generate sufficient airflow at and around the source to capture and draw in the contaminant-laden airThe process, source and contaminant cloud are outside the hood26All capture hoods work on the same principles regardless of size27Calculation of rate of ventilation air flow

Q = H/(60 * CP * * t) = H/1.08 * tWhereH = Heat removed in Btu/hrt = indoor outdoor temperature difference(oF)CP = 0.245 Btu/lb/ oF = 0.075 lb/ft328Application Of Industrial Ventilation SystemsOptimization of energy costs.Reduction of occupational health disease claims.Control of contaminants to acceptable levels.Control of heat and humidity for comfort.Prevention of fires and explosions.