Safety
This section covers Safety. The exam tests hazard recognition at treatment plants, wells, distribution sites, and laboratories: chemical exposure, confined spaces, excavation, electrical work, and emergency response.
Core rules
- Use the hierarchy of controls: eliminate or substitute the hazard, then engineer controls, administrative controls, and PPE last.
- Confined space entry requires a permit, isolation, atmospheric testing, ventilation, an attendant, and rescue arrangements. Test oxygen first, then flammables, then toxics.
- Common entry limits are oxygen 19.5–23.5%, flammable gas below 10% LEL, hydrogen sulfide at or below 10 ppm, and carbon monoxide at or below 35 ppm; follow your permit and meter instructions.
- Chlorine gas is heavier than air and irritating at low concentrations. Ammonia is lighter. Never mix chlorine and ammonia or acid without controlled procedures.
- Trenches 5 ft or deeper require a protective system unless in stable rock; provide ladders and keep spoil back from the edge.
- Lockout/tagout protects workers from pumps, mixers, chemical feeders, and electrical energy.
Worked example
A meter reads oxygen 19.0%, H2S 5 ppm, and LEL 0%. The space is oxygen-deficient, so entry is prohibited even though the toxic and flammable readings look acceptable. Ventilate, retest, and do not enter until oxygen is within 19.5–23.5% and all readings meet the permit. Reasoning: oxygen deficiency alone can cause collapse; acceptable H2S does not cancel it.
Traps
Entering to rescue without PPE or backup; testing toxics before oxygen; using pure oxygen to ventilate; storing chlorine and ammonia together; leaving trench spoil at the edge; bypassing lockout to test equipment.