A mobile (rolling) scaffold is mounted on casters. It is constructed of a tubular-metal section of scaffolding or is made of components. designed specifically for a particular purpose (fig. 4-31).

The following are safety rules that pertain to scaffolding:

Inspect all equipment before use.

Inspect erected scaffolds regularly to ensure they are being maintained in a safe condition.

Provide adequate sills for scaffold posts and use baseplates.

Plumb and level scaffolds as erection proceeds, so the branches fit without having to be forced.

Fasten all braces securely.

Use and install scaffolding accessories according to the procedure recommended by the manufacturer.

Do not alter accessories in the field.

Do not ride on rolling scaffolds.

Remove all types of material and items of equipment from the platform before attempting to move a scaffold.

Figure 4-31. - Aluminum ladder scaffold.

Q16. Banks or sides of a trench of what height must be shored or sloped?

WASTEWATER SYSTEMS

LEARNING OBJECTIVE: Understand wastewater component application and wastewater system installation.

A wastewater system is a group of sewer pipes and pumps designed to convey domestic and industrial wastes and to transport them to a wastewater treatment plant (fig. 4-32). The wastewater system starts in a house or building that conveys wastewater, known as a house sewer, into a "lateral" sewer pipe. The sewer main receives wastes from two or more laterals. The trunk sewer is a large pipe that receives the flow from laterals and mains. When gravity flow is no longer practical or possible, a lift station is used to pump wastewater to a higher level. A forced main (pressure main) carries the discharge from the lift station to the main or trunk sewer. From here, the wastewater flows by gravity to an interceptor sewer, connecting into the wastewater treatment plant. An outfall sewer is a pipe that carries the treatment plant effluent to the point of final discharge.

A wastewater system safeguards the public health by preventing communicable diseases from getting into groundwater or drinking water systems. The wastewater system carries the raw wastewater to the treatment plant quickly for treatment. The wastewater system should only be carrying domestic and industrial wastes. Infiltration (leakage or seepage of water from a storm or groundwater into a sewer) should be controlled to the lowest practical limit. Good monitoring and maintenance are required to control infiltration. Too much infiltration overloads both the wastewater system and the treatment plant. The end result is not enough detention time and a washout of wastewater solids.

MATERIALS

As a Utilitiesman, you may be involved in construction of a wastewater system and in maintenance, repair, or minor replacement of sewers. The joints and seals used for each type and size of pipe are important. Leaks and breaks often occur at the joints; therefore, with fewer joints and proper seals, leaks can be reduced. The pipe chosen for the wastewater system should be based on the type of waste, the kind of soil, the estimated flow, and the weight of the backfill.