11-CS-2 Engineering Communications · May 2019
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams — May 2019 — 11-CS-2 Engineering in Society: Health and Safety. Closed book. Do any five of the seven questions (each 10 marks); a bonus question (5 marks) may be attempted in addition. Full essay-type answers are expected. Complete answers to all seven questions and the bonus follow.
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
The NFPA 704 "hazard diamond" is four coloured squares, each rated 0 (minimal) to 4 (severe):
The numbers are therefore a severity rating on a common 0–4 scale, one per hazard category, so that a responder can judge all three hazards at a glance without knowing the chemical's identity. Reading the example diamond printed with part (a): Red 4 — extremely flammable, vaporizes and burns readily at ordinary temperatures; Blue 2 — intense or continued exposure could cause temporary incapacity or residual injury; Yellow 1 — normally stable but can become unstable at elevated temperature and pressure; white blank — no special hazard declared.
The cargo diamond reads (as restated on the paper): Health = 1 (slight health hazard), Flammability = 2 (ignites on moderate heating—directly relevant, since the engine fire is spreading toward the cargo), and Instability/Reactivity = 0 (stable; does not react even with water). The paper restates these three values in case the black-and-white reproduction is poor; the white block on the printed diamond is blank, so the material carries no special (e.g., oxidizer or water-reactive) hazard.
Danger to the fire crew: the principal hazard is fire growth and flammable cargo. A flammability rating of 2 means the cargo will ignite once moderately heated, so the spreading engine fire can readily set the load alight, enlarging the fire. Because the material is stable (reactivity 0), the danger is not a violent chemical reaction but rather: the intense heat of a growing flammable-cargo fire; toxic and irritating products of combustion (the health-1 rating, plus whatever the burning material yields); and the risk of container/tank rupture or a BLEVE if sealed containers are heated by the fire. A slight (1) direct health hazard still warrants respiratory protection.
Precautions: approach from upwind and uphill; establish an exclusion zone and evacuate the public; wear full turnout gear with SCBA against heat and combustion products; cool exposed containers/tanks with water spray to prevent rupture/BLEVE; fight the fire with an agent suited to the flammable material (foam or water fog to blanket/cool a flammable liquid, or dry chemical); prevent runoff from reaching drains/waterways; and, crucially, identify the exact material from the shipping papers, placard and UN number before committing, since only the hazard ratings—not the identity—are known from the diamond.
Possible material: a moderately flammable, slightly hazardous, stable material consistent with Flammability 2, Health 1, Reactivity 0 and no special hazard—most likely a combustible liquid such as diesel fuel, kerosene, fuel oil, or a paint/solvent (these have flash points in the "moderate heating" range, a slight health hazard, and are chemically stable). Note that a violently water-reactive substance (e.g., sodium or calcium carbide) would carry a high reactivity rating and a barred-W symbol, which is inconsistent with the Reactivity = 0 shown here—so a water-reactive material is ruled out by the ratings themselves.
