Work , Study and Ergonomics , Fire and Fire safety , Engineering Drawing and Safety , General studies , UPSC ESE

 Work , study and ergonomics:

• Ergonomics : ergo + nomics
• It is a science that deals with job , task or workplace suitable for worker so that the physical nature of work and physical capacity of worker are compatible to each other.
• Ergonomic design is necessary in order to avoid injuries to tissues , ligaments , tendons, etc of the worker otherwise the worker may develop musculoskeletal disorder (MSD) , cumulative disorder (CTD). eg: awkard and static posture , repetitive motion , forceful exertion.

Symptoms of MSD/CTD

• Pain , numbness tingling
• Loss time to work
• Temporary or permanent disability
• Reduces productivity

Application of ergonomics : man - machine - system

Factors causing MSD/CTD

1.Risk inherited  in the worker:

• Workage : once a person enters workage he/she will develop stresses in the body
• Gender : right gender at right work
• Strength and endurance : ability of muscle or muscle group to remain contracted for along period of time. it can be of two types : isometric and isotonic
• Physical fitness : if worker is physically unfit then chances of injury is more
• Anthropometry: science that deals with body size and its proportion like BMI. deviation in BMI leads to change in work pattern.

2. Risk factor inherent in task/job

• Required force : the required force for doing work depends on various factors like type of grip , nature of surface , weight or size of object, etc.
• Vibration : long exposure to vibration interfere sensory receptors. it can be segmental vibration , whole body vibration.
• Posture : position at which work is done. eg wrist extension , tendinities, arm stretched over shoulder, bending.

3. Risk factor in the workplace and environment

• Heartstress : working in environment like engines , welding , thermal plants needs exposure to heat for the worker . Hence worker may dehydrate or faces electrolytic imbalance or get heat stroke.
• Cold stress : inability of body to maintain adequate temperature when working in cold environment known as hypothermia.
• Light : lighting in the work place must be according to the nature of work 
• Noise : it is unwanted sound and exposure to it may result to either temporary and permanent disability.

Controlling risk factors:

• Elimination and substitution : eliminate conventional method and substitute modern technology
• Engineering control: work station redesign , designing machine to fit worker.
• Administrative control : scheduling more breaks , right person at right work , curtailing overtimes.

Fire safety:

Chemistry of fire:

Elements of fire:

1) Oxygen : it sustains combustion

2) Heat : it raises the material above ignition temperature

3)Fuel : it supports combustion

To sustain fire there must be a chain reaction amongst all the three elements:

To stop the fire , any of the elements has to be removed or the chain reaction between the elements need to be stopped.

1. Cooling : to cool down the ignition temperature by using either water jets , portable fire , extinguishers.
2. Smothering : to cut off the supply of oxygen 
3. Starvation : to remove the fuel from  the site

Stages of fire growth:

1.Incipient stage or initiation stage:

• It is early stage of fire growth and this stage give a fair idea of how fire will grow depending upon the fire material at this stage.
• There is no detectable flames at this stage and fire can be extinguished with fire extinguisher.

2. Growth stage:

• Sufficient amount of oxygen and fuel are available
• The heat developed may moves upward of the confined space from ceiling it moves laterally.
• Visibility is best at ground level

Flash over:

• Sufficient oxygen + fuel
• Ceiling temperature rises to 500 - 600 degree celcius and hence due to high heat developed the remaining fuel achieve ignition temperature within 3 - 4 seconds
• Sudden transition from growth stage to fully developed stage.
• Due to high pressure of burning gases , the openings of confined space like windows , doors , etc, move out with substantial velocity.

3. Fully developed stages:

All the combustible material is ignited and hence heat release is at maximum aslso known as fire load.

4.Decay stage:

• Due to insufficient oxygen and fuel the fire extincts and turns to ashes after a long period of time.
• Before turning to ashes and after fire extinction the fuel remains as glowing embers.

Rules for fighting fire : RACE

R - rescue : rescue the trapped person from fire and call out fire

A - alarm : activate the nearest alarm system

C - confine : confine the area by closing the openings so that fire does not spread

E - extinguish : extinguish the fire without risking life else evacuate the place.

Types of fire and fire extinguisher:

Note :

• CO2 must not be used in confine space as it replaces oxygen and hence choking is experienced
• Dry powder is universal fire extinguisher
• Before using water the cause of fire must be known else the fire may become more dangerous or pose threat to life.

Use of fire extinguishers:

• P - pull : pull the pin
• A - aim : aim the nozzle at the base of fire 
• S - squeeze : squeeze the lever so that fire extinguishing agent comes out
• S - sweep : sweep the nozzle at the base of fire

Safe building evacuation: fire escape

General equipment:

Exit access : access to nearest exit like lobbies , corridors

• Fire door:

1. It is used to confine heat , toxic gases so that it does not spread to exit area. 
2. It should be heat resistant of at least one hour. it must be openable from the one side and the width of door . 
3. It must be 1 metre and self closing type.the fire door if connected to main cooridoor than it must open inward.

• Horizontal exit :
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1. It is made between the buildings or compartment having more than one exit.
2. It is having two side openable and self closing doors having fire resistance of 1 hour.
3. Such type of exit is seen in hospitals , malls , etc

Note : In case of fire , lift must not used because its function is interrupted due to power failure caused by fire.

Exit : exit connects exit access to exit discharge

eg staircase

• A building of height greater than 15 metre or having an area of 500 square metre must be equipped with two stair case of which one should be inside of building and other outside.
• The external stair case must be made of fire resistant material and it must lead to open space.

Exit discharge: exit that discharges to open space

Characteristics of fire exit:

• Properly designed without any obstruction should be providing to having adequate capacity and the designated exit must not be closed i.e. always unlocked.
• Protection of entire path to egress from fire , smoke and toxic gases .
• Provision of adequate and reliable fire alarm system 
• Adequate illumination and ventilation with proper marking of egress with green colour.
• Atleast two exit for each floor and one for each room should be provided

Types of fire extinguisher

• Sprinklers
• Fire hydrants
• Deluge in oil industry , power plant
• Water mist fire extinguisher
• Stand pipe fire extinguisher