18-Env-B6 Agricultural Waste Management · December 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams, December 2018 — 18-Env-B6, Agricultural Waste Management (3 hours, open book, all 15 questions to be attempted, 100 marks total).
Reference texts: Rynk et al., On-Farm Composting Handbook (NRAES-54); OMAFRA, Nutrient Management Act, 2002 and O. Reg. 267/03 / Nutrient Management Protocol (NMAN); Metcalf & Eddy, Wastewater Engineering (anaerobic digestion chapter); ASABE Standards (manure storage, land application equipment); Environment and Climate Change Canada / Canada–Ontario Lake Erie Action Plan.
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.
Drag-hose lines routinely run hundreds of metres to over a kilometre from the pump to the applicator, and clearing a plugged line with compressed air introduces several serious hazards if not carefully controlled.
1. Projectile / blockage-ejection hazard. A large compressor can build substantial pressure behind a blockage before it clears; when the plug finally releases, it is ejected from the open end of the hose at very high velocity along with a slug of pressurized manure — this has caused documented serious injuries and fatalities on farms when a worker was positioned near the discharge end (or the coupling itself failed) at the moment of release. The open end must be securely anchored, aimed into a safe/empty area, and kept clear of all personnel before pressurizing the line.
2. Hose whip and coupling/fitting failure. A drag hose is not necessarily rated for the full pressure a large compressor can develop, especially against a full blockage (effectively a closed-end condition); over-pressurizing can rupture the hose or blow apart a coupling, and the sudden release of stored pneumatic energy causes violent, unpredictable hose whip that can strike a nearby worker. A pressure-relief valve sized below the hose's rated working pressure, and a maximum-pressure limit set on the compressor itself, are essential controls.
3. Sudden release of trapped manure gases. The manure remaining in the line (and any pocket behind the blockage) can accumulate H₂S, methane and other decomposition gases in the same way a foam pocket does (Questions 11 and 13); when the line clears, this gas is released suddenly and can reach hazardous concentrations in the immediate area, particularly if the work is being done in a low-lying or poorly-ventilated location.
4. Uncontrolled manure spray / environmental release. Once the plug clears, the pressurized line can discharge a large volume of manure very quickly over a wide area, well beyond what a controlled, gravity/pump-fed application would deliver — this is both a worker-exposure hazard (direct contact, slip hazard) and a potential unauthorized discharge/spill if it reaches a ditch, tile inlet or watercourse.
Safe practice requires: using compressed air only per the hose/coupling manufacturer's rated pressure and procedure, fitting and verifying a pressure-relief device, securely anchoring and clearing the discharge end before pressurizing, keeping all personnel out of the line-of-fire and away from couplings under pressure, and treating the operation as a controlled hazardous-energy release (similar in spirit to the lockout/confined-space precautions of Question 13) rather than a routine maintenance task.
