The Bitter Almonds That Weren't (Probably)
08:40 Monday. A facilities manager calls 911 reporting "a strong chemical smell" on the third floor of a 12-story office building. Fire/EMS arrive to find 22 people outside with burning eyes, cough, and runny nose; three are vomiting; one woman has audible stridor and is drooling. A custodian says he poured a bucket of sodium hypochlorite into a floor drain "to clear a smell," and a co-worker then added muriatic acid to the same bucket, roughly 20 minutes ago. The HVAC is running, staff are still self-evacuating through the lobby, and a TV crew has set up across the street. Two evacuees tell a police officer the smell was "like bitter almonds." You have four SCBA-equipped firefighters in structural turnout gear and one EMS supervisor. The nearest hazmat team is 35 minutes out.
1. State your working agent assessment and explain how the "bitter almond" reports should - and should not - change it.
Read the worked answer
Working assessment: chlorine (or a mixed chlorine/chloramine irritant gas), not cyanide.
Reasoning for chlorine first:
- A credible, time-linked source mechanism: hypochlorite + muriatic acid liberates chlorine gas. This is the single most common chemical-release mechanism in buildings.
- The syndrome fits an irritant gas with high water solubility: immediate burning eyes, cough, rhinorrhea, and - critically - stridor and drooling, which point to upper-airway edema and are not typical early findings in cyanide.
- Chlorine is denser than air, so symptoms clustering on a lower floor with a floor-drain source is coherent.
Why the odor reports must not drive the assessment:
- The ability to detect cyanide's bitter-almond odor is genetically variable; a meaningful fraction of people cannot smell it at all, and those who can may be reporting a false positive from other nitriles or cleaning products. Two reports out of 22 is not a signal.
- Anchor on physiology and epidemiology, not odor. The exam question is whether you will abandon a well-supported hypothesis for a dramatic one.
What keeps cyanide on the list:
- Enclosed-space combustion or a mixed release can generate cyanide. If a patient develops cardiovascular collapse, severe lactic acidosis, or seizures out of proportion to airway findings, treat empirically for cyanide (hydroxocobalamin) while continuing supportive care. Do not wait for a lab.
Net: manage as an unknown irritant gas with chlorine as the leading hypothesis; prepare antidote and airway resources for the alternative.
2. Command asks whether the four SCBA-equipped firefighters should enter the third floor to sweep for remaining occupants. Give your recommendation with reasoning.
Read the worked answer
Recommendation: a tightly bounded, on-air sweep only if there is a specific, credible indication people are trapped; otherwise hold, isolate, and ventilate.
Reasoning:
- Protection is partial. SCBA protects the airway, but structural turnout gear is not vapor- or splash-protective against chlorine. The entry team's skin is exposed. This is a Level B respiratory problem, not a fire problem.
- The hazard is being generated, not dissipated. The source is a floor drain where acid and hypochlorite are still reacting. Concentration near the source is unknown and may be IDLH; the PID on scene cannot quantify chlorine.
- The rescue benefit is speculative. 22 people have already self-evacuated. Every other occupant is ambulatory and has the same egress path. Committing four people in inadequate suits for a speculative search trades a certain responder risk for an uncertain benefit.
- If you do enter: two-in/two-out with a dedicated backup team at the door, full SCBA, a hard turnaround time set by a safety officer, a lifeline or radio check at fixed intervals, and no entry below the level of the release without a plan.
Operational alternative: use the building PA and phone bridge to direct remaining occupants to the nearest stairwell, pressurize or isolate the stairwell, shut down HVAC recirculation to stop distribution, and wait for the hazmat team. Keep occupants out of the lobby - it is on the plume's path.
3. Police want to hold the custodian and treat the floor as a crime scene; the building manager wants reoccupancy by 17:00. What do you advise?
Read the worked answer
Advise unified command with two parallel objectives: hazard control first, evidence preservation as a constraint - and no reoccupancy on a clock.
On the custodian:
- His account is currently the best source hypothesis, which makes him a witness and a potential subject at the same time. Do not let scene cleanup proceed in a way that destroys the bucket, the drain, or the mixing location.
- Interviewing, detention, and criminal characterization are law-enforcement decisions, not the IC's. Your job is to tell the police what physical evidence matters and to keep the hot zone intact.
On the 17:00 deadline:
- Reoccupancy must be tied to pre-defined clearance criteria, not to a schedule. Odor is not a clearance criterion - olfactory fatigue and individual variation make it useless.
- Practical criteria: instrument readings at background at multiple points with a calibrated device appropriate to the suspected agent, confirmed source control (drain flushed/isolated under controlled conditions), and documented ventilation.
- Note the reporting obligations that run in parallel: the release may exceed a reportable quantity and may trigger environmental notification for the storm drain if wash water was used.
Say plainly to the building manager: "We will clear the building when the criteria are met; we cannot tell you that will be 17:00." Then give the next update time.