What should you know? Electrical safety

Grade 9 Science

Content

• Circuits must be complete for electrons to flow

Curricular competencies

Questioning and predicting

• Demonstrate a sustained intellectual about a scientific topic or problem of personal interest

Processing and analyzing data and information

• Experience and interpret the local environment

Applying and innovating

• Contribute to care for self, others, community, and world through individual or collaborative approaches
• Transfer and apply learning to new situations
• Generate and introduce new or refined ideas when problem solving
• Contribute to finding solutions to problems at a local and/or global level through inquiry

Communicating

• Communicate scientific ideas, information, and perhaps a suggested course of action for a specific purpose and audience, constructing evidence-based arguments and using appropriate scientific language, conventions, and representations
• Express and reflect on a variety of experiences, perspectives, and worldviews of place

Electricity always seeks the easiest path to the ground and will travel there through any conductive material. Even we conduct electricity and if we get between electricity and the ground or something touching the ground, electricity will flow through us. A person standing on a tree, a ladder or the floor is connected to the ground and can be shocked.

Electricity travels very quickly

Electricity travels at approximately 300,000 km per second. You aren’t given the slightest warning and there is no time to react.

Grounding

Grounding refers to intentionally connecting a circuit to the ground in order to prevent the build-up of voltage that can be hazardous to connected equipment or to people. The third prong of a plug provides this ground connection.

Ripple effect

If anything makes contact with a high-voltage power line, or if a broken power line falls to the ground or lands on a vehicle, electricity will flow to the ground, then spread out in concentric circles like the ripples in a pool of water.

Voltage is very high at the point where electricity makes contact with the ground. The level of intensity decreases as the distance increases from the point of contact. A safe voltage of zero  begins approximately 10 metres (the length of a bus) from the point of contact.

Step potential

Due to the difference in voltage as you move towards or away from a source of electricity, it is possible to “step” between high- and low-voltage differences if one foot is in a higher voltage area than the other foot. Because the human body is usually a better conductor of electricity than the ground, the electricity can flow between feet through the body, sometimes causing serious injury or death. This is referred to as “step potential.”

Touch potential

Trees can be very conductive. If a tree comes into contact with a high-voltage power line and a person is touching the tree, or touching a ladder leaning against the tree, there will be a high-to-low voltage difference between the person and the ground. This will force electrical current to flow through the person to the ground and can result in serious injury or death. This is referred to as “touch potential.”

Shuffle or hop

If the ground becomes energized, you can avoid shock by keeping your feet close together and taking short, shuffling steps, never allowing the heel of one foot to move beyond the toe of the other, until you are at least 10 metres away from the energized area.

Alternatively, you can hop with both feet together to a minimum distance of 10 metres. Shuffling is the better method because it is possible to fall while hopping, especially if you are on uneven ground. Falling will most likely result in parts of your body touching areas with different electrical potentials, allowing electricity to flow through your body.

Electrical injuries

Injuries can occur through direct contact with electrical energy or when electricity arcs (jumps) through a gas (such as air) to a person who is grounded. High-voltage contact burns can damage internal tissues while leaving only very small injuries on the outside of the skin. Muscle contractions, or a startled reaction, can cause a person to fall from a ladder, scaffold or aerial bucket. The subsequent fall or dropping of a piece of equipment can cause serious injuries.

Injuries are classified in three ways:

1. Electrocution (fatal)
2. Electric shock
3. Burns

• Review and assess the students’ "What should you know? Electrical safety" worksheet for completeness and accuracy.
• Review and assess the students’ peer evaluations for an accurate assessment of their own participation in the group and of the group’s presentation.
• Assess the groups’ presentations for accuracy and the equal participation of all members, using the "Group work evaluation rubric".