Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
National Exams — December 2019 — 11-CS-2 Engineering in Society: Health and Safety. Closed book. Do any five of the seven questions (each 10 marks). Full essay-type answers are expected; sketches may support the explanations. Complete answers to all seven questions follow.
Note on the reference charts. Questions 2 and 7 depend on the two attachment pages: page 6 is the Brauer/Dalziel chart of the effects of 60 Hz AC current on a 150 lb (68 kg) man, and page 7 is the Fine risk-assessment nomograph. The nomograph prints only the qualitative descriptors (no numbers appear on its Likelihood, Exposure or Consequence axes), so the scale points used below (Likelihood 10 / 6 / 3 / 1 / 0.5 / 0.1, Exposure 10 / 6 / 3 / 2 / 1 / 0.5, Consequence 100 / 40 / 15 / 7 / 3 / 1) are the standard Fine–Kinney values that the chart's own axis spacing reproduces. Selecting a descriptor for each activity is a matter of judgement; the choices are stated explicitly below and reasonable justified alternatives are equally acceptable, as the paper's Note 8 permits.
Method (Fine): $\text{Risk} = \text{Likelihood}\times\text{Exposure}\times\text{Consequence}$. The chart on page 7 is an alignment nomograph: a straight line is drawn from the chosen point on the Likelihood axis through the chosen point on the Exposure axis and extended to the Tie Line; a second straight line is then drawn from that tie point through the chosen point on the Possible Consequences axis and extended to the Risk Score axis, where the score is read. The scale points the chart's axes carry are Likelihood 10 / 6 / 3 / 1 / 0.5 / 0.1, Exposure 10 / 6 / 3 / 2 / 1 / 0.5 and Consequence 100 / 40 / 15 / 7 / 3 / 1 (each listed from the most to the least severe descriptor: Likelihood and Consequence are printed in that order from top to bottom, but the Exposure axis runs the other way, with Very rare at the top and Continuous at the bottom), so drawing the lines and multiplying the three values give the same answer. Choosing the descriptor for each factor is a judgement; the choices are stated below and reasonable justified alternatives are acceptable.
(a) Risk Scores
(i) Coal-mine drilling operator: Likelihood = quite possibly could happen (6) — the coal-face environment (methane, roof, explosives) makes an incident realistically possible; Exposure = frequent/daily (6); Consequence = very serious (potential fatality, 15; a gas/dust explosion could be a multi-fatality disaster).
$$\text{Risk}_{\text{miner}} = 6 \times 6 \times 15 = \boxed{540} \;\Rightarrow\; \text{VERY HIGH RISK (consider discontinuing / major correction)}$$
(ii) Petrochemical shift supervisor (walk-around): Likelihood = unusual but possible (3); Exposure = frequent/daily (in the plant each shift, 6); Consequence = serious injury (7) for the routine walk (a major release could be higher).
Reading these off the chart. For the supervisor the construction lands on the Risk Score axis at about 126, between the printed 100 and 200 ticks and inside the Substantial risk band. For the miner the construction runs off the top of the printed scale: the axis is labelled only as far as 500, and 540 is above it, so the line is extended past the top tick and the reading is reported as “above 500” — which is unambiguously inside the Very high risk — consider discontinuing operation band, the band the top of the axis carries. (Recording it as > 500 rather than as a spot value on the axis is the honest way to present it; the product 540 is what the chart's own scale points give.) The coal-mine operator scores far higher—driven by the higher likelihood and the fatal potential of the mining environment at the same daily exposure.
(b) Hazards
Coal-mine driller: methane gas and coal-dust explosion; roof/rock fall (ground failure); respirable coal dust and silica (pneumoconiosis/"black lung"); noise and hand–arm vibration from the drill; oxygen deficiency/poor ventilation; proximity to explosives; electrical hazards; poor lighting; and confined, restricted egress.
Petrochemical supervisor: exposure to toxic and flammable chemicals and possible releases; fire/explosion; slips, trips and falls on the walk-around; moving vehicles/equipment; noise; hot surfaces/steam; and working across a large, hazardous site.
(c) Minimising the Hazards
Coal-mine driller: continuous methane monitoring and adequate ventilation; flameproof/intrinsically safe equipment and control of ignition sources; dust suppression (water/wet drilling) plus respiratory protection; roof support/ground control; strict blasting procedures; noise/vibration controls; training, gas detectors, communication and escape/rescue provisions. These lower both the likelihood and the consequence.
Petrochemical supervisor: personal gas detector and area monitoring; appropriate PPE; safe, well-lit walking routes segregated from traffic with good housekeeping; permit-to-work systems and process safety controls; communication and emergency procedures; and training. These reduce exposure and likelihood.
