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Ergonomics and Design for Human Use (workshop)

Case Study

~ Gitesh Nandanwar

INTRODUCTION “ Understanding ergonomics at work “ * We may have heard of the term ‘ergonomics’ * This is sometimes referred to as ‘human factors’ * Not everyone really understands what ergonomics is, what it does, or how it affects people.

WHAT IS ERGONOMICS ? Ergonomics is a science concerned with the ‘fit’ between people and their work. It puts people first, taking account of their capabilities and limitations. Ergonomics aims to make sure that tasks, equipment, information and the environments suit each worker. To assess the fit between a person and their work, ergonomist have to consider many aspects. * The job being done and the demands on the worker * The equipment used (its size, shape, and how appropriate it is for the task). * The information used (how it is presented, accessed and changed). *The physical environment (temperature, humidity, lighting, noise, vibration), and * The social environment (such as teamwork and supportive management).

Ergonomists consider all the physical aspects of a person, such as: * Body size and shape; * Fitness and strength; * Posture, * The senses, especially vision, hearing and touch, * The stresses and strains on muscles, joints, nerves.

Ergonomists also consider the psychological aspects of a person, such as: * Mental abilities, * Personality, * Knowledge, and * Experience. By assessing these aspects of people, their jobs, equipment, and working environment and the interaction between them, ergonomists are able to design safe, effective and productive work systems.

How can ergonomics improve health and safety? Applying ergonomics to the workplace: * Reduces the potential for accidents, * Reduces the potential for injury and ill health, * Improves performance and productivity.

What kind of workplace problems can ergonomics solve? Ergonomics is typically known for solving physical problems. For example, ensuring that work surfaces are high enough to allow adequate clearance for a worker’s legs. However, ergonomics also deals with psychological and social aspects of the person and their work. For example, a workload that is too high or too low, unclear tasks, time pressures, inadequate training, and poor social support can all have negative effects on the person and the work they do.

How do I identify ergonomic problems? There are many ways in which ergonomic problems can be identified. These can range from general observations and checklists to quantitative risk assessment tools. * Talking to employees and seeking their views. Employees have important knowledge of the work they do, any problems they have, and their impact on health, safety, and performance, * Assessing the work system by asking questions such as: - Is the person in a comfortable position? - Does the person experience discomfort, including aches, pain, fatigue, or stress? - Is the equipment appropriate, easy to use and well maintained? - Is the person satisfied with their working arrangements? - Are there frequent errors?

What can I do if I think I have identified an ergonomic problem? * Look for likely causes and consider possible solutions. A minor alteration may be all that is necessary to make a task easier and safer to perform. For example: - provide height-adjustable chairs so individual operators can work at their preferred work height, - remove obstacles from under desks to create sufficient leg room - arrange items stored on shelving so those used most frequently and those that are the heaviest are between waist and shoulder height, - raise platforms to help operators reach badly located controls, - change shift work patterns, and - introduce job rotation between different tasks to reduce physical and mental fatigue. * Talk to employees and get them to suggest ideas and discuss possible solutions.

Anthropometric Measurements Anthropometry is the science that measures the range of body sizes in a population. When designing products it is important to remember that people come in many sizes and shapes. Anthropometric data varies considerably between regional populations. For example, Scandinavian populations tend to be taller, while Asian and Italian populations tend to be shorter.

Common Workplace Postures There are common postures found in the office environment that can be considered when designing workplace products or space. This section reviews guidelines for these postures: * Standing, * Sitting, * Reaching, and * Moving.

* Standing: Some users may need or want to stand while at their workstations. If this is the case, an appropriate desk can be designed and selected for the type of work being performed. Desk height for a standing operator can range from 28-43" depending on whether the desk is for precision, light, or heavy work. When selecting desk height it is important to remember that the top line of text on a computer monitor should be located at eye level or slightly below.

* Sitting: Correct seated posture is a continual debate with ergonomic professionals. Some say that users need to have a 90-90-90 degree placement for the elbow, hip, and knee joints, respectively. Others feel that a variation in this placement is better, as long as it does not lead to slouching or hunching over. A good seated posture is one that is comfortable and does not put a lot of stress or strain on the user’s buttocks, back, or arm muscles, and allows the user’s feet to be on the floor.

* Reaching: While sitting or standing, an individual at work will usually have to reach for something. The workstation, and parts that go with workstations (such as overhead storage and pedestals), should allow the majority of movement of the user’s body joints within healthy zones. When designing products, consider how much individuals will have to reach in order to minimize awkward or unhealthy positions.

* Moving: Users will move around in their environment to file papers, answer a phone, or stretch. An occasional break from sitting is encouraged because it helps to stimulate muscles, and increases blood flow, which decreases fatigue. The space in a cubicle or desk area should allow the chair to move around easily. Also, a wheelchair may need to turn around or move in the office space, requiring a 60" diameter turning radius and at least 36" of passage width Chairs and other devices in the workspace can allow the user to easily get up and move around without having to move armrests, adjust other chair settings, or put undue stress on the body.


FIRE EXTINGUISHERS Fire extinguishers are designed to put out or control small fire, if not shocked immediately. will soon spread out of control. In fact, most big fires start out as small ones. it is important, therefore, that we equip our workplace with the proper fire extinguisher as part of our fire protection plan.

HISTORY Fire extinguishers, in one form or another, have probably postdated fire by only a short time. The more practical and unitized extinguisher now commonplace began as a pressurized vessel that spewed forth water, and later, a combination of liquid elements. The older extinguishers comprised cylinders containing a solution of baking soda (sodium bicarbonate) and water. Inside, a vessel of sulfuric acid was positioned at the top of the body. This design had to be turned upside down to be activated, so that the acid spilled into the sodium bicarbonate solution and reacted chemically to form enough carbon dioxide to pressurize the body cylinder and drive out the water through a delivery pipe. This volatile device was improved by placing the acid in a glass bottle, designed to be broken by a plunger set on the top of the cylinder body or by a hammer striking a ring contraption on the side to release the acid. Cumbersome and sometimes ineffective, this design also required improvement.

DESIGN Aside from using different agents, manufacturers of extinguishers generally use some type of pressurized vessel to store and discharge the extinguishing agent. The means by which each agent is discharged varies. Water fire extinguishers are pressurized with air to approximately 150 pounds per square inch (psi)—five times a cartire pressure—from a compressor. A squeeze-grip handle operates a spring-loaded valve threaded into the pressure cylinder. Inside, a pipe or "dip tube" extends to the bottom of the tank so that in the upright position, the opening of the tube is submerged. The water is released as a steady stream through a hose or nozzle, pushed out by the stored pressure above it. Water extinguishers of the "gas cartridge" type operate in much the same manner, but the pressure source is a small cartridge of carbon dioxide gas (CO 2 ) at 2,000 psi, rather than air. To operate a gas cartridge unit, the end of the extinguisher is struck against the floor, causing a pointed spike to pierce the cartridge, releasing the gas into the pressure vessel. The released CO 2 expands several hundred times its original volume, filling the gas space above the water. This pressurizes the cylinder and forces the water up through a dip-pipe and out through a hose or nozzle to be directed upon the fire. This design proved to be less prone to leakdown (loss of pressure over time) than simply pressurizing the entire cylinder.

In foam extinguishers, the chemical agent is generally held under stored pressure. In dry powder extinguishers, the chemicals can either be put under stored pressure, or a gas cartridge expeller can be used; the stored-pressure type is more widely used. In carbon dioxide extinguishers, the CO 2 is retained in liquid form under 800 to 900 psi and is "self-expelling," meaning that no other element is needed to force the CO 2 out of the extinguisher. In halon units, the chemical is also retained in liquid form under pressure, but a gas booster (usually nitrogen) is generally added to the vessel.

RAW MATERIALS Fire extinguishers can be divided into four classifications: Class A, Class B, Class C, and Class D. Each class corresponds to the type of fire the extinguisher is designed for, and, thus, the type of extinguishing agents used. Class A extinguishers are designed to fight wood and paper fires; Class B units fight contained flammable liquid fires; Class C extinguishers are designed to fight live electrical fires; and Class D units fight burning metal fires.

Current Fire Extinguisher Colour Codes




Paper, wood, textiles & solid materials fires

DON'T Liquid, electrical or USE metal fires

POWDER Liquid, electrical wood, paper & textile fires Metal fires



Liquid, paper, wood & textile fires

Liquid & Electrical fires

Electrical or metal fires

Metal fires

Previous Extinguisher Colour Codes






1. Both colour codes are still in use 2. A new Class F extinguisher is now available for cooking oil and fat fires SEPS, University of Glasgow 2001

Water has proven effective in extinguishers used against wood or paper fires (Class A). Water, however, is an electrical conductor. Naturally, for this reason, it is not safe as an agent to fight electrical fires where live circuits are present (Class C). In addition, Class A extinguishers should not to be used in the event of flammable liquid fires (Class B), especially in tanks or vessels. Water can cause an explosion due to flammable liquids floating on the water and continuing to burn. Also, the forceful water stream can further splatter the burning liquid to other combustibles. One disadvantage of water extinguishers is that the water often freezes inside the extinguisher at lower temperatures. For these reasons, foam, dry chemical, CO 2 , and halon types were developed.

Foam, although water based, is effective against fires involving contained flammable liquids (Class B). A two-gallon (7.5 liters) extinguisher will produce about 16 gallons (60 liters) of thick, clinging foam that cools and smothers the fire. The agent itself is a proprietary compound developed by the various manufacturers and contains a small amount of propylene glycol to prevent freezing. It is contained as a mixture in a pressurized cylinder similar to the water type. Most aircraft carry this type of extinguisher. Foam can also be used on Class A fires.

The dry powder agent was developed to reduce the electrical hazard of water, and thus is effective against Class C fires. (It can also be used against Class B fires.) The powder is finely divided sodium bicarbonate that is extremely free-flowing. This extinguisher, also equipped with a dip-tube and containing a pressurizing gas, can be either cartridge-operated or of the stored pressure type as discussed above. Many specialized dry chemical extinguishers are also suitable for burning metal fires, or Class D.

Carbon dioxide (CO 2 ) extinguishers, effective against many flammable liquid and electrical fires (Class B and C), use CO 2 as both the agent and the pressurizing gas. The liquified carbon dioxide, at a pressure that may exceed 800 psi depending on size and use, is expelled through a flared horn. Activating the squeeze-grip handle releases the CO 2 into the air, where it immediately forms a white, fluffy "snow." The snow, along with the gas, substantially reduces the amount of oxygen in a small area around the fire. This suffocates the fire, while the snow clings to the fuel, cooling it below the combustion point. The greatest advantage to the CO 2 extinguisher is the lack of permanent residue. The electrical apparatus that was on fire is then more likely to be able to be repaired.

* Halon, at least in fire extinguishers, may soon become a footnote to history. The aluminum pressure vessel is made by impact extrusion. In this process, the aluminum block is put into a die and rammed at high velocity with a metal casting tool. The force liquifies the aluminum and causes it to flow into the cavity around the tool, thus forming the open-ended cylinder. This cylinder is then finished in necking and spinning processes, which form the open end of the cylinder. Most of the other elements of a fire extinguisher are made of metal. The pressure vessel is generally made of an aluminum alloy, while the valve can either be steel or plastic. Other components, such as the actuating handle, safety pins, and mounting bracket, are typically made of steel.

The Manufacturing Process Manufacture of the tank-type or cylinder fire extinguisher requires several manufacturing operations to form the pressure vessel, load the chemical agent, machine the valve, and add the hardware, hose, or nozzle.

Creating the pressure vessel * 1: Pressure vessels are formed from puck-shaped (disc) blocks of special aluminum alloy. The puck is first impact extruded on a large press under great pressure. In impact extrusion, the aluminum block is put into a die and rammed at very high velocity with a metal tool. This tremendous energy liquifies the aluminum and causes it to flow into a cavity around the tool. The aluminum thus takes the form of an open-ended cylinder with considerably more volume than the original puck.

Necking and spinning * 2: The necking process puts a dome on the open end of the cylinder by constricting. In a typical gas-cartridge extinguisher, a spike pierces the gas cartridge. The released gas expands quickly to fill the space above the water and pressurize the vessel. The water can then be pumped out of the extinguisher with the necessary force. The open end with another operation called spinning. Spinning gently rolls the metal together, increasing the wall thickness and reducing the diameter. After spinning, the threads are added. * 3: The vessel is hydrostatically tested, cleaned, and coated with a powdered paint. The vessel is then baked in an oven where the paint is cured.

Adding the extinguishing agent * 4: Next, the extinguishing agent is added. If the vessel is a "stored-pressure" type, the vessel is then pressurized accordingly. If a gas-cartridge is necessary to help expel the extinguishing agent, it is also inserted at this time. * 5: After the extinguishing element is added, the vessel is sealed and the valve is added. The valve consists of a machined body made of metal bar stock on a lathe, or a plastic injected molded part on the economy versions. It must be leak free, and it must have provisions for threading into the cylinder.

Final assembly * 6: The final manufacturing operation is the assembly of the actuating handle, safety pins, and the mounting bracket. These parts are usually cold formed—formed at low temperatures —steel or sheet metal forms, purchased by the manufacturer from an outside vendor. Identification decals are also placed on the cylinder to identify the proper fire class rating as well as the suitability for recharging. Many of the economy versions are for one time use only and cannot be refilled.

Quality Control All fire extinguishers in the India fall under the jurisdiction of the National Fire Protection Association (NFPA), Under-writer's Laboratories, The Coast Guard, and other organizations such as the indian Fire Department. Manufacturers must register their design and submit samples for evaluation before marketing an approved fire extinguisher. One of the most crucial checkpoints during the manufacturing process occurs after the extinguishing agent is added and the vessel sealed. It is extremely important that the cylinder not leak down the pressurizing gas, because that would render the extinguisher useless. To check for leaks, a boot is placed over the cylinder to serve as an accumulator. A trace gas is released inside, and within two minutes any unacceptable rate of leakage can be recorded by sophisticated pressure and gas-detecting equipment. All extinguishers are leak tested. The Future With the gradual elimination of halon, a new, non-damaging agent will most likely replace the hazardous chemical within the next few years. In addition, new applications of the old designs are being seen; most prevalent are automatic heat and fire sensors that discharge the extinguisher without the need for an operator.

Workshop on “ ERGONOMICS & DESIGN FOR HUMAN USE “ The workshop at NID, Ahmedabad Anchor faculty : Dr Subir das. Group assignment Subject : Case study on Fire Extinguisher

The given dry powder fire extinguisher we observed following points, such as: Positive Point.

Cylendrical Shape

Easily Visible pressure

Good Color Scheme

Simply Hanged

Negative Point.

Extra force Required .. Uncomfortable lever releaser

No Support for holding or caring

Bad readability of instruction

Instruction color quality


font visibility


was not good

on spinel cord

Sharpe corner ..










Regulator Meter Guage Adjustable Belt Expiry date on front side Instruction / cautions information. Handle Adjustment

Lever Information in numerical & not in words

Bottom [plastic fiber]

* Neutral Posture * Reduce Extra Force * Everything in easy reach * work at proper height * minimum static load * minimize pressure points * provide clearance

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