Class: Senior Secondary School 2 (SS2 / SSS 2)
Term: 1st Term
Week: 7
Age: 16 years
Duration: 45 minutes
Subject: Metal Work
Curriculum Theme: Pre-Vocational Studies
Previous Lesson: Introduction to Welding.
Topic: Oxy-Acetylene Welding Equipment
Subject Matter: Oxy-acetylene welding equipment (cylinders, blowpipe, rubber hose, regulators), hazards in welding operations, flashback arrestor

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

Define oxy-acetylene welding.
Identify the main components of oxy-acetylene welding equipment.
State the function of each component, including the flashback arrestor.
List common hazards associated with welding operations.

Affective Domain:

Appreciate the importance of safety measures in welding.
Value the correct handling and maintenance of welding equipment.
Show concern for personal and environmental safety during welding.

Psychomotor Domain:

Point out the various parts of oxy-acetylene welding equipment if available.
Describe the correct procedure for connecting welding equipment components.

Collaborate with peers in identifying welding equipment.
Participate in discussions about safe welding practices.

Reference Materials

The following resources were used in planning this lesson:

Senior Secondary Schools Education Curriculum
State Unified Scheme of Work
Metalwork for Senior Secondary Schools by A.O. Adegoke
https://www.education.gov.ng/curriculum/
https://www.waecdirect.org/curriculum/

Instructional Materials

The teacher will teach this lesson with the aid of:

Gas cylinders (oxygen and acetylene, if available or pictures)
Regulators
Rubber hoses
Blowpipe (torch)
Flashback arrestor (actual or diagram)
Safety goggles and welding gloves (as examples of PPE)
Charts or diagrams illustrating the complete oxy-acetylene welding setup

Rationale for the Lesson

This lesson helps pupils understand the tools and safety needed for oxy-acetylene welding. It prepares them to safely identify and handle welding equipment, which is important for practical tasks in metal fabrication and for understanding workplace safety.

Prerequisite/Previous Knowledge

Pupils should have basic knowledge of metal fabrication, different types of metals, and general workshop safety rules.

Lesson Content/Board Summary

Oxy-Acetylene Welding Equipment

Introduction to Oxy-Acetylene Welding

Oxy-acetylene welding is a process that uses the heat generated by burning a mixture of oxygen and acetylene gases to melt and join metals. It is also known as gas welding or oxy-fuel welding.

Components of Oxy-Acetylene Welding Equipment

The main components required for oxy-acetylene welding are:

Gas Cylinders:
- Oxygen Cylinder: Contains oxygen gas under high pressure. It is usually black and has right-hand threaded valve connections.
- Acetylene Cylinder: Contains acetylene gas dissolved in acetone under moderate pressure. It is usually maroon (red) and has left-hand threaded valve connections to prevent accidental mixing.
Regulators: Devices attached to the cylinders to reduce the high cylinder pressure to a safe working pressure for the torch. Each regulator has two gauges: one for cylinder pressure and one for working pressure.
Rubber Hoses: Flexible tubes that transport oxygen and acetylene from the regulators to the blowpipe. Oxygen hoses are typically green or black, while acetylene hoses are red.
Blowpipe (Torch): The tool used to mix the oxygen and acetylene gases and deliver the flame to the workpiece. It consists of a handle, mixing chamber, and interchangeable nozzles for different flame sizes.
Flashback Arrestor: A safety device fitted between the regulators and the blowpipe. Its purpose is to prevent a reverse flow of gases (flashback) from the torch back into the hoses and cylinders, which could cause an explosion.

Hazards in Welding Operations

Welding operations involve several potential dangers. Common hazards include:

Burns: Caused by direct contact with the flame, hot metal, or sparks.
Eye Damage: Intense light from the flame can cause arc eye or permanent vision damage if proper eye protection is not worn.
Inhalation of Fumes and Gases: Welding fumes can contain harmful particles and gases that can affect the respiratory system.
Fire and Explosion: Flammable materials in the vicinity of welding can ignite. Flashbacks can lead to explosions of gas cylinders.
Electric Shock: (Less common in oxy-acetylene but a general welding hazard) From faulty electrical equipment.
Noise: High levels of noise from certain welding processes can cause hearing damage.

Safety Precautions in Oxy-Acetylene Welding

To ensure safety during oxy-acetylene welding, the following precautions should be taken:

Always wear appropriate Personal Protective Equipment (PPE), including welding goggles or a face shield, welding gloves, flame-resistant clothing, and safety boots.
Ensure adequate ventilation in the welding area to disperse fumes.
Check all equipment (hoses, regulators, blowpipe) for leaks or damage before use.
Always use flashback arrestors on both oxygen and acetylene lines.
Keep flammable materials away from the welding area.
Store gas cylinders upright and secure them to prevent them from falling.
Open cylinder valves slowly.
Always follow the manufacturer’s instructions for equipment operation and maintenance.

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils, reviews the previous lesson, and introduces the topic: “Oxy-Acetylene Welding Equipment,” explaining its relevance in metalwork.
Pupils’ Activity: Pupils respond to greetings, recall the previous lesson, and listen attentively to the introduction.
Learning Point: Pupils are prepared for the new lesson and understand its importance.

Step 2: Identification of Cylinders and Regulators

Time: 7 minutes
Teaching Skill: Explanation/Demonstration
Teacher’s Activity: The teacher displays pictures or actual gas cylinders and regulators. The teacher explains the function of each type of cylinder (oxygen and acetylene) and how regulators work to control gas pressure.
Pupils’ Activity: Pupils observe the materials, identify the cylinders and regulators, and listen to the explanations of their functions.
Learning Point: Pupils identify gas cylinders and regulators and understand their basic functions.

Step 3: Explanation of Hoses and Blowpipe

Time: 7 minutes
Teaching Skill: Explanation/Visualisation
Teacher’s Activity: The teacher shows the rubber hoses and blowpipe (or diagrams). The teacher explains their purpose, the colour coding of the hoses, and the parts of a blowpipe.
Pupils’ Activity: Pupils observe the hoses and blowpipe, noting their features and colour codes, and describe their uses.
Learning Point: Pupils understand the roles of hoses and the blowpipe in delivering and mixing gases.

Step 4: Understanding the Flashback Arrestor

Time: 6 minutes
Teaching Skill: Concept Explanation
Teacher’s Activity: The teacher introduces the flashback arrestor, explaining its critical role as a safety device and where it is connected in the welding setup.
Pupils’ Activity: Pupils listen carefully and ask questions to clarify the function and importance of the flashback arrestor.
Learning Point: Pupils understand the importance and function of the flashback arrestor in preventing accidents.

Step 5: Discussion on Welding Hazards

Time: 7 minutes
Teaching Skill: Question and Answer/Discussion
Teacher’s Activity: The teacher leads a discussion on potential hazards associated with oxy-acetylene welding, prompting pupils to think about risks.
Pupils’ Activity: Pupils identify and discuss various hazards such as burns, eye damage, fumes, and fire risks.
Learning Point: Pupils recognise the dangers involved in welding operations.

Step 6: Safety Precautions

Time: 6 minutes
Teaching Skill: Explanation/Listing
Teacher’s Activity: The teacher explains necessary safety precautions, including the use of PPE, proper ventilation, and equipment checks.
Pupils’ Activity: Pupils listen, list the safety measures, and discuss how to apply them.
Learning Point: Pupils learn about essential safety measures to prevent accidents.

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

What is oxy-acetylene welding?
List four main components of oxy-acetylene welding equipment.
State the function of a gas regulator.
Explain the purpose of a flashback arrestor.
Mention three hazards associated with welding operations.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 2 minutes
Teaching Skill: Summarisation
Teacher’s Activity: The teacher summarises the key points of the lesson, re-emphasising the importance of safety. The teacher then gives pupils an assignment to draw a labelled diagram of an oxy-acetylene welding setup.
Pupils’ Activity: Pupils listen to the summary and copy down the assignment.
Learning Point: The lesson is reinforced, and pupils are given a task to consolidate their learning.

Lesson Keywords

Oxy-acetylene – A gas welding process using oxygen and acetylene.
Welding – The process of joining materials, usually metals or thermoplastics, by causing fusion.
Cylinders – High-pressure containers for storing oxygen and acetylene gases.
Regulators – Devices that control the pressure of gases from cylinders to the blowpipe.
Blowpipe – The tool that mixes and directs the oxygen and acetylene flame.
Flashback arrestor – A safety device that prevents reverse gas flow and explosions.
Hazards – Potential sources of harm or danger.

Differentiation

For pupils who grasp concepts quickly, the teacher can encourage them to research different types of welding nozzles and their uses. For pupils needing more support, the teacher can provide simplified diagrams and allow peer-to-peer explanation of equipment functions.

Note for teachers using this lesson plan

Teachers should ideally use actual oxy-acetylene welding equipment for demonstration, if available and safe to do so, to enhance practical understanding. Emphasize safety procedures thoroughly, as welding involves significant risks. Encourage pupils to ask questions and discuss real-life scenarios where this equipment is used.