The investigators are stumped. There appears to be no evidence of forced entry, no apparent malice, yet the two parents and two children are found dead in the comfort of their own home.
Finally, a sharp, young investigator discovers the truth — accidental carbon monoxide poisoning — and the book’s title then holds a deeper, double meaning.
Carbon monoxide (CO) is downright deadly.
A byproduct of combustion, CO is produced by common household appliances such as gas or oil furnaces, clothes dryers, water heaters, ovens, and ranges. CO can also be produced by a charcoal grille operating in an enclosed area, a fire burning in a fireplace, or a car running in an attached garage.
It is odorless and tasteless. It’s absorbed by our lungs through normal breathing and can asphyxiate the unsuspecting.
This poisonous gas is considered enough of a threat that the Consumer Product Safety Commission and the National Association of Fire Chiefs have officially recommended that each residential dwelling have at least one carbon monoxide alarm.
Time of exposure and concentration of the gas in the air are the key factors governing the alarms. With CO exposure, a person’s hemoglobin (the oxygen carrier in the blood stream) is altered to the deadly carboxyhemoglobin.
For us humans, time is definitely not on our side, since our systems readily accept carbon monoxide over the life-giving oxygen atoms (as much as 200 times quicker than oxygen).
Therefore, the detector’s response time is based on a medical equation which combines the number of minutes of exposure and the concentration of carbon monoxide in the air, which is measured in parts per million (ppm).
Underwriters Laboratories (UL) has published the most widely followed standard (UL 2034) for predetermined levels at which a carbon monoxide detector must respond in alarm. (See Table 1.)
This technology is based on a rate-of-change principle. When exposed to CO, the sensing elements absorb photons at a rate dependent on the concentration of the CO in the environment. By monitoring the rate of change in the amount of light transmitted through the sensing elements, the concentration of CO in the surrounding environment can be accurately determined. The sensing elements also get lighter when CO decreases.
This sensor also has a built-in “humidity buffer” that maintains a constant humidity level around the sensor to accommodate for shifts in humidity. A change in the humidity level may cause a sensor to operate improperly.
The gas mixes with the electrolyte solution, causing the electrode to generate a current that causes the circuit to create a voltage in proportion to the amount of CO sensed, thereby triggering the alarm.
1. The 120-V hardwire alarm is permanently wired to a household’s main power. It is typically used in new construction or remodeling applications, where connecting to an electrical box is easier.
Hardwire CO alarms can be single or multiple station. Multiple-station alarms are interconnected (usually up to 12 alarms) so that all will sound even if only one alarm detected CO.
2. The 120-V hardwire with 9-V battery backup functions just like the above, with the added security of a battery backup in cases where there is risk of a power outage.
3. Relying solely on a building’s main power, 120-V direct-outlet plug-ins are simple to install; just plug them into a wall outlet.
4. The 120-V direct-outlet plug-in models with 9-V battery backup are similar to the above, but have the added security of a battery backup in cases where there is a risk of power outage.
5. Finally, battery-operated CO alarms provide the greatest freedom from the electrical system and the greatest flexibility for location of the units.
To the consumer, having a properly placed alarm offers valuable protection from CO poisoning, the “senseless killer.”
For the contractor, CO detectors are another product that can help bind you to your customers, through interest for their health and well-being.