"...Police and firefighters who responded were initially unaware that hydrogen-cyanide was involved; four police officers, 13 firefighters, and a medical examiner required medical treatment..."¹

"...A city detective and a police officer, who were assigned to investigate the incident, arrived at the scene between 6:00 and 7:00 p.m. (about three hours after the victim was extricated from the vault). They were admitted onto the grounds by an unidentified plant employee, who led them to the valve vault and removed the manhole cover. Seeing blood on the wall at the bottom of the vault, the detective decided to enter to get dimension measurements but shortly afterward 'came up for air, gasping.' Thinking he was only having a claustrophobic reaction, the detective attempted to enter the valve vault again..."²

"...Realizing that the trench walls remained unstable and hazardous, they warned others to keep out of the trench and waited for the police who arrived approximately three minutes later. A police officer entered the trench and saw the victim through a two to three-inch gap between the fallen section of earth and the trench wall."³

Investigations and evidence collection can take one into unusual settings including inside confined spaces such as trash compactors, storm sewers, underground vaults, and into deep excavations or trenches. Many locations may appear relatively benign but can hold hidden hazards with potentially fatal consequences for any who enter unprepared. These hazards can include, depending on conditions; lack of oxygen, toxic or flammable gases, risk of entrapment/engulfment, physical or mechanical hazards, and crushing or entombment from soil collapse.

Review of literature shows many citations of death among law enforcement agencies from entering these spaces unprotected. Fatalities and injuries usually occur in confined spaces and excavations for three basic reasons:

1) failure to recognize the area as potentially hazardous,
2) failure to monitor the potential hazards, and
3) failure to control those hazards identified.

OSHA considers (29 CFR 1910.146), a “confined space” to be:

1) an enclosed area large enough for personnel to enter and work; and
2) with limited or restricted means for entry or exit; and
3) not designed for continuous employee occupancy.

OSHA considers a trench or excavation (OSHA Subpart P of 29 CFR 1926) to be regulated when more than four feet deep. At this depth, there is potential for sidewall collapse and accumulation of hazardous atmospheres and the trench must be evaluated by a “competent person” before entry.

Normal air is about 20.9% oxygen, 78.1% nitrogen, and 1% argon with small amounts of various other gases. The composition of air in trenches and confined spaces can be changed by both natural and man-made activities. Use of industrial or piped chemicals, welding activities, or old hazardous materials spills might affect the composition of air as well as the natural products of biological decomposition. The composition is usually affected in two ways, either there is a toxic contaminant or the oxygen is displaced by the chemical. When these confined spaces have the potential hazard of holding or generating atmospheric hazards, it becomes a “Permit-Required Confined Space” according to OSHA. These spaces may not be entered until the atmosphere has been evaluated by a competent person. Typically the air is tested with a “4-Gas meter,” a calibrated, direct-reading instrument for oxygen and other contaminants as appropriate for the site conditions. These typically include carbon monoxide, flammable gases and vapors, and hydrogen sulfide.

Hydrogen sulfide (H2S) is a common product of natural decomposition. It is a colorless, extremely toxic gas that smells like rotten eggs. Initially it has good warning properties. Most people can detect the odor at low levels—less than one parts per million (ppm)—but olfactory fatigue can quickly occur. Once this happens one no longer smells it leading to the mistaken belief that the “gas has cleared.” Exposure to levels over 1,000 ppm are possible and can result in nearly instant coma and death. Heavier than air, it can accumulate in underground confined spaces and excavations. Other gases such as carbon dioxide are particularly insidious as they are odorless and thus have no “warning properties.” These can occur naturally through biological and chemical decomposition and may also displace air in sewers, storage bins, wells, and tunnels.