Chapter 6: Safety Hazards

Always address safety requirements before entering the laboratory environment.
Four specialized hazard categories highlighted in this chapter:
- Use of Electrical Equipment
- Use of Radioactive Substances
- Use of Lasers
- Use of Fuel Gas
Core principle: Proactive planning, proper installation, and rigorous supervision prevent accidents.

All electrical work (installation, alteration, inspection, testing, repair) must be done by contractors registered with the Electrical & Mechanical Services Department.
Provide an effective earthing (grounding) system for every installation.
Install a main switch capable of isolating power to all outlets in the laboratory.
Use switched socket outlets (preferably with pilot lights) to allow local isolation.
- Position outlets away from water sources to reduce splash risk.

Even small currents through the body can trigger fatal heart failure.
- Currents above $0.01\ \text{A}$ can cause severe shock.
- Currents above $0.03\ \text{A}$ are considered lethal.
In typical school laboratories the supply is fixed at $220\ \text{V}$ ; current through the body therefore depends on body resistance.

Use three-pin plugs conforming to national safety standards.
Keep adaptors/extension units to an absolute minimum.
Reject any plug, adaptor, or extension showing cracks, loose parts, discoloration, charring, or deformation (signs of overheating).

Never handle appliances with wet hands, wet feet, or while standing on a wet floor.
Verify that appliance voltage rating matches the supply voltage before use.
Switch off both appliance and supply before inserting or withdrawing a plug.
An appliance giving even a slight shock requires immediate repair.
Do not leave appliances switched on and unattended.
Store flammable liquids away from electrical equipment; vapours could ignite from arcs/sparks.
Charge secondary cells (e.g.
lead-acid batteries) only in well-ventilated areas to disperse hydrogen gas.

Cover floors with effective insulating mats during high-voltage experiments.
No one works alone with high voltage.
Provide protective screens/barriers to block accidental contact.
Unless specifically instructed otherwise, connect the negative terminal of an Extra-High-Tension (EHT) supply to earth.

Governed by the Code of Practice on the Use of Radioactive Sources for Teaching Purposes in Schools (Radiation Board).

Students must never be exposed to ionising radiation without a valid instructional rationale.
Any exposure must be kept As Low As Reasonably Achievable (ALARA).
Only sealed sources are allowed, and only for simple experiments.
No deliberate exposure of any person is permitted.
Plan experiments to minimise exposure time.

A designated source custodian (graduate science staff) supervises all sealed sources.
Custodian performs annual checks (≤12-month intervals) on source condition.
Classroom teacher must account for all sources before class ends.
A source may be used by a student only under direct teacher supervision.
Sources shall not leave school premises without Radiation Board approval.

Keep only the minimum practicable activity/quantity of sources; never exceed exemption limits:
- Cobalt-60, Strontium-90, Radium-226, Americium-241:
- Max two sources per isotope
- Activity ≤ $200\ \text{kBq}$ each
- Insoluble Radium-226 for diffusion cloud chamber:
- Max 10 sources
- Activity < $750\ \text{Bq}$ each
Store all sources in a locked metal container with a permanent radiation warning label.
Access limited to authorised staff.
Store each source in separate, clearly labelled compartments; each must be easily identifiable.

Transport sources inside dedicated containers between storage and lab.
Use tongs or forceps; never bare hands.
Handle alpha emitters with extreme care due to high ionisation potential.
Maintain > $30\ \text{cm}$ distance from body; always direct source away from people.

Defective, obsolete, or unnecessary sources should be disposed of promptly:
- Return to supplier and notify Radiation Board; or
- Dispose of by a method approved by Radiation Board.
The Radiation Board Secretary must be notified in writing within 48 hours of any damage, loss, or disposal.

A laser emits a collimated, coherent, monochromatic beam (visible or invisible).
Even low-power lasers can cause permanent eye damage; strict controls mandatory.

Appoint a graduate science teacher as laser custodian (procurement, storage, issuance, return, maintenance of safety gear).
Teacher-in-charge drafts and enforces laser safety rules and operating procedures.
Every user must be trained and familiar with both operation and safety protocols.

Students reminded: Never view laser source directly or indirectly; no skin exposure to direct beam.
Use non-reflective or absorbing materials around the beam path to avoid specular reflections.
If reflections are inevitable (e.g. at lenses), install protective screens:
- Non-flammable, optically opaque, matt grey finish.
All personnel in laser area wear appropriate, wavelength-specific protective goggles.

Position beam above or below eye height of seated/standing students.
Rigidly fix laser so beam direction cannot shift inadvertently.
Never align beam with power on; perform alignment with laser off or at lowest possible power.

Post warning signs inside & outside laser area and on access doors when laser is energized.
Keep room brightly lit to minimise pupil dilation.
Brief students on local setup; they must stand behind the laser when firing and stay > $1\ \text{m}$ from any part of the experiment.
Switch off laser immediately after use and lock away when not in operation.

On accidental exposure: close eyes immediately, turn head away.
Report any exposure (or suspected exposure) to instructor; seek medical attention at once.