VENTILASI TRI MARTIANA

INTRODUCTION A good and effective ventilation system

is necessary in a workplace which have processes that emit air contaminants such as dust, fumes, mists or vapours.

Substitution or enclosure method Simple, cheap and effective

TYPES OF VENTILATION

Natural General Dilution

LEV

NATURAL VENTILATION Natural movement of air entering and

leaving openings such as windows, doors, roof ventilators as well as through cracks and crevices of a building

Heated air rises, cool air below

USE OF NATURAL VENTILATION

Not suitable for processes which emit dust, fumes, mists or gas

Rooms for chemical storage + 25% of floor area Half the ventilating area should be

between floor level and a height of 2.25m from the floor

GENERAL VENTILATION A method of improving or maintaining the

quality of air in the work environment with airflow

A room or an entire building is flushed by supplying and exhausting large volumes of air throughout the area

1. Supply or forced ventilation

2. Exhaust or induced ventilation

VENTILATION dilution

ventilationdilutes

contaminant to an acceptable level

comprises fans set in walls or roof

cheap and simple limited

application as a control strategy

local exhaust ventilationcaptures

contaminant close to point of generation

comprises hood, ductwork, filter, fan,outlet

good control of hazardous contaminants

DILUTION VENTILATION (I) changes the whole workplace air over a

given time period ie air changes per hour

limit to circumstances where:exposure limit is high low evaporation rate for liquidsslow evolution for gasesoperators not close to the point of

generationsubstance is quickly carried away from the

operator

DILUTION VENTILATION (II) rate of contaminant generation governs

air changes per hour required density of contaminant governs position

of fans:density >1 (ie solvents) - low level fan in

walldensity <1 (ie hot gases) - high level fan in

roof problems include:

“dead areas” where poor airflow allows contamination to build up

heat losses due to high rate of air change

DILUTION VENTILATION (DV) DV consists of general ventilation Uncontaminated outside air + inside air

= diluting and reducing the concentration of air contaminants to acceptable levels to which a worker can be safely exposed for eight hours a day

DV is prohibited – control emission of very toxic air contaminants e.g., formaldehyde or other carcinogenic chemicals

For effective DV, the exhaust outlet and air supply must be so located that all the air employed in the ventilation passes through the zone of contamination

USE OF DILUTION VENTILATION

DV is usually applied to the control of contaminants in situation meeting these criteria:

To control vapours (+organic) from low toxicity solvents

To control contaminants released over such a large area or in such a manner that LEV is impossible, impractical or prohibitively expensive

LOCAL EXHAUST VENTILATION (I) Hood or exhaust inlet

receptor hood contaminant directed into a large hood by fan

assisted draughtcaptor hood

contaminant captured by air flow close to point of generation low pressure large volume flowhigh pressure low volume flow (high velocity)

LOCAL EXHAUST VENTILATION (II) ducting

straight with gentle bends and angled jointssufficient air flow to prevent deposition of

solidsaccess ports for cleaning and flow

monitoring filter or purifying system

cyclones, washers, electrostatic, bag filters

LOCAL EXHAUST VENTILATION (III) Fans

axial flow fan airflow is parallel to the shaft of the impeller compact and fits neatly into ductwork

centrifugal fan air enters the impeller then is discharged at right

angles exhaust outlet

careful location to avoid: cyclic pollution effects of weather of air disturbance

LEV Capture or contain contaminants at their

source before they escape into the work room environment

System consists of one or more hoods, ducts, air cleaner and a fan

LEVs remove contaminants rather than just dilute them

USE OF LEV The most effective means of controlling

air contaminants is to capture and remove the air contaminants at their source with LEV and to prevent them from being carried away by air currents into the breathing zones of the worker

Major release (toxic) of localized sources of contaminants.

LEV consists of 4 parts:

1. Hoods (most important)

2. Ducts

3. Air cleaner device

4. Fan and motor

HIGH PRESSUREVENTURI

The hood consists of 3 main types to contain and remove the air-borne contaminants.

1. Enclosures

2. Capturing hoods

3. Receiving hoods

CONCLUSION Ventilation – an effective way to control

toxic air contaminants if substitution or enclosure method of control is not possible

DV reduces contaminant concentrations by diluting them with fresh air. (not for toxic emission)

LEV capture or contain contaminants at their source before they are dispersed in the workroom

LEVs need to be maintained, inspected and tested regularly to ensure that it is performing adequately