18-Env-B6 Agricultural Waste Management · December 2019
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
National Exams, December 2019 — 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 the residual manure from a line by blowing compressed air through it introduces several serious hazards if not carefully controlled.
1. Projectile / plug-ejection hazard. A large compressor can build substantial pressure behind any remaining slug of manure or a partial blockage before it clears; when it 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 a coupling 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 while the line is still effectively closed at the far end; 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 can accumulate H₂S, methane and other decomposition gases in the same way a foam pocket does (Question 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 line clears, the pressurized air can discharge the remaining 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.
