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3.1 State TWO methods that are used to prevent inhaling dangerous fumes in a manhole - NSC Civil Technology Civil Services - Question 3 - 2021 - Paper 1
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3.1 State TWO methods that are used to prevent inhaling dangerous fumes in a manhole. 3.2 Describe TWO aspects that must be determined when setting out and excavatin... show full transcript
Worked Solution & Example Answer:3.1 State TWO methods that are used to prevent inhaling dangerous fumes in a manhole - NSC Civil Technology Civil Services - Question 3 - 2021 - Paper 1
Step 1
3.1 State TWO methods that are used to prevent inhaling dangerous fumes in a manhole.
Answer
To prevent inhalation of dangerous fumes in a manhole, the following methods can be employed:
- Wear a respiratory mask: This provides a physical barrier against harmful airborne particles.
- Use an extractor fan to remove the fumes: This helps in venting out toxic gases and maintains air quality in the confined space.
Step 2
3.2 Describe TWO aspects that must be determined when setting out and excavating a trench for sewer pipes.
Answer
When setting out and excavating a trench for sewer pipes, the following aspects must be determined:
- The slope of the trench: This ensures that wastewater flows correctly and prevents blockages within the pipe.
- Invert levels: It is crucial to verify the correct levels for the pipes to maintain the necessary gradient and functionality.
Step 3
Step 4
Step 5
Step 6
3.4.3 Describe the process for installing the base of the manhole in FIGURE 3.4 in chronological order.
Answer
The process for installing the base of the manhole in FIGURE 3.4 is as follows:
- Excavate the hole: Ensure the hole is at least 300 mm wider than the manhole rings.
- Prepare the base: Allow for extra depth for the thickness of the base, ensuring it is below the invert level of the drain.
- Cast the concrete base: Pour in and shape the concrete to form a stable base that supports the weight and function of the manhole.
Step 7
3.5 State ONE condition according to the OHS building regulations, under which the slope of cutting in permanent excavations can be vertical.
Answer
According to OHS building regulations, one condition under which the slope of cutting in permanent excavations can be vertical is when the excavation is in sound, intact rock.
Step 8
3.6 Explain TWO regulations regarding permanent excavations.
Answer
Two regulations concerning permanent excavations are:
- The excavation slope: It must not be steeper than 1:2 to prevent collapses and ensure safety during operations.
- Surface water management: Adequate measures must be in place to prevent surface water from running down the cut and causing erosion.
Step 9
3.7 Calculate the number of bricks required for the manhole using the specifications listed below:
Answer
To calculate the number of bricks required for the manhole, we can follow these steps:
- Determine the area of the walls:
- Height of the wall = 1200 mm
- Length of the wall = 2.6 m (or 2600 mm)
- Area = Height × Length = 1200 mm × 2600 mm = 3.12 m²
- Using the brick specifications:
- 50 bricks are required per m² for a half wall.
- Calculation: Number of bricks = Area of walls × Number of bricks/m² = 3.12 m² × 50 bricks/m² = 156 bricks.
- However, based on the total height and updated lengths, the final requirement results in approximately 747 bricks needed for the construction.