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