23-Ind-B10 Workplace Health and Safety · December 2018
Question 6 of 7: Methods and Placement of Hazard Controls, and Choosing the Best Method
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
Notes on this paper
National Exams — December 2018 — 17-Ind-B10 Workplace Health and Safety. Closed book; no calculators permitted. Any five of the seven questions constitute a complete paper; all questions are of equal value (20 marks each). Answers are written in point form but fully, as instructed. Complete answers to all seven questions follow, with assumptions stated where the question invites them.
Reference texts: Brauer, Safety and Health for Engineers, 4th ed.; CCOHS (Canadian Centre for Occupational Health and Safety), OSH Answers: Hazard Control and OSH Answers: Ventilation; CCPS (Center for Chemical Process Safety), Guidelines for Risk Based Process Safety; CSA Z1002 Occupational health and safety — Hazard identification and elimination and risk assessment and control; CSA Z432 Safeguarding of machinery; ACGIH, Industrial Ventilation: A Manual of Recommended Practice.
Question 6: Methods and Placement of Hazard Controls, and Choosing the Best Method (20 marks: 7/6/7)
(i) Key Methods for Controlling Hazards in the Workplace
As established in Question 2(iii), the key methods form the hierarchy of controls, ranked from most to least effective:
Elimination — physically removing the hazard from the workplace entirely.
Substitution — replacing the hazard with a less hazardous alternative material, process, or piece of equipment.
Engineering controls — guards, enclosures, ventilation, and interlocks that isolate people from the hazard independent of behaviour.
Administrative controls — procedures, training, signage, permits, scheduling, and job rotation that change how and when people are exposed.
Personal protective equipment (PPE) — equipment worn by the individual worker as the last line of defence.
(ii) The Three Areas Where Controls Can Be Placed
Beyond ranking controls by method, controls can also be classified by where in the exposure pathway they act — the classic source–path–receiver model:
At the source — controlling the hazard where it is generated or originates (enclosing a noisy machine, reducing a process's operating pressure or temperature, using a quieter or less hazardous piece of equipment in the first place). This is generally the most effective placement, since it prevents the hazard from ever entering the workplace environment.
Along the path — controlling the hazard between the source and the worker, once it has already left the source but before it reaches the person (local exhaust ventilation capturing airborne contaminant before it disperses, a barrier or distance separating a worker from a radiation source, sound-absorbing material in the path between a machine and a workstation).
At the receiver (the worker) — controlling exposure at the point of the worker themselves, when source and path controls have not fully eliminated the hazard (enclosed/soundproofed control booths, PPE, administrative limits on time spent in the exposure area). This is the least reliable placement, since it depends on the control being consistently used/maintained by or around the individual worker.
This source–path–receiver framework is largely orthogonal to, but overlaps with, the hierarchy of controls in part (i): elimination and substitution act only at the source, engineering controls can act at the source, along the path, or at the receiver (an enclosure vs. a booth), and PPE acts only at the receiver.
(iii) How the Best Method Is Chosen; Whether More Than One Can Be Used, and Why
Selecting the control method (or combination of methods) follows a structured evaluation, not a single fixed rule:
Start at the top of the hierarchy and work down — the "best" single control, when feasible, is always the highest tier that is technically and economically achievable for the specific hazard, since it removes the largest share of risk with the least dependence on ongoing human behaviour.
Assess technical feasibility — whether elimination/substitution is even possible without compromising the process (a hazardous chemical intermediate may be technically unavoidable to a given product), and whether an engineering control can physically achieve the required exposure reduction.
Assess cost and practicality — capital cost, maintenance burden, and impact on production, weighed against the magnitude of the risk being controlled — a very low-probability, low-severity hazard may not justify the highest-tier control, while a high-severity hazard usually justifies a substantial one regardless of cost.
Assess residual risk after each candidate control — whether the control, once applied, actually brings the risk to an acceptable/tolerable level (per the risk evaluation criterion of Question 4(i)-B), or whether residual risk remains that a further or additional control must address.
Yes, more than one control method is routinely applied together, for two reasons:
Defence in depth — no single control tier is perfectly reliable on its own (an engineering control can fail or be defeated, a procedure can be skipped under pressure), so layering an engineering control with an administrative backup and PPE means a single control's failure does not, by itself, result in an injury.
Residual risk after a higher-tier control is often not yet acceptable — e.g., substitution reduces but does not eliminate a chemical hazard, so an engineering (ventilation) control and administrative/PPE measures are still layered on top to bring the remaining exposure down to the tolerable level.
The choice is therefore not "one control," but the combination of tiers that, taken together, brings the residual risk to an acceptable level at a feasible cost — with the highest-tier control in that combination always doing the heaviest lifting.
