Some time ago, I watched an interesting TV murder mystery program. It had a most intriguing plot. The scenario involved a wealthy man who had his home office designed such that it was similar to an impenetrable vault—both for security and privacy purposes. The room was so secure that it had its own air supply and other essential life-sustaining amenities for extended periods of seclusion.

However, this well-designed, perfectly secure room became a murder weapon in itself because someone who was displeased with the man added a halon gas canister to the ventilation system. The man was murdered by asphyxiation when the gas canister was remotely activated and halon gas pumped into the room. This action temporarily replaced the room’s normal atmosphere, thus depriving the man of life-sustaining oxygen.

As you can imagine, it took considerable time and a complicated investigation to determine the cause of death since the room was locked from the inside and there was no evidence of foul play.

Of course, I made some notes and researched halon gas! I found that, for a long time, halon gas was the gold standard of fire-suppressant systems for enclosed areas such as bank vaults, museums and other secure areas that contained high-value assets that could be damaged by traditional water-based sprinkler systems. Although, the halon in the television plot was not part of a fire suppression system for that man’s office, it was attached to the fresh air supply used specifically for his isolated office space.

I also learned that halon gas production was banned in many countries between 1989 and 1994 when it was discovered that halocarbon agents depleted the ozone layer. Existing halon-based fire suppression systems are still permitted, and recycled halon gas is allowed for maintenance and to refill these systems as needed, but no new halon systems can be constructed.

So, my idea of a storyline involving halon gas in one of my future stories became less feasible, since halon is not as available as it used to be. I decided that the TV show writers were possibly working from older research data.

That’s when I dug deeper and searched for halon replacement products. I discovered that, after halon was banned, other “clean agent” systems were developed that reportedly have no known ozone-depleting capacity. And these systems are installed now in place of, or as replacements for, halon-based systems.

These mainly include various inert gas fire suppression systems that utilize mostly nitrogen, argon or carbon dioxide—plus a few other inert elements that appear to be more difficult to use.

Nitrogen, argon and carbon dioxide naturally occur in the atmosphere, they do not harm the environment and are not toxic to humans (at least to the extent regarding residues on surfaces after their use).

Therefore, it’s perfectly feasible that any of these three gases could be used in a murder plot in much the same way as halon gas was used in that TV program. Flood a secure, sealed area with one of these gases and any human within that environment would die from oxygen depletion since the gases replace the regular room air to suppress fire without damaging valuables. This effect requires an airtight environment, of course, and that is termed “enclosure integrity.”

An interesting advantage to these inert gases is that the gas canisters that contain them can be located much further away from the protected enclosure than halon canisters. These inert gases flow much better inside suppression system piping and can be located up to 400 feet away from the area to be protected against fire.

This fact makes it easier for the villain in your murder plot to have access to the equipment that supplies air to the secure area to add an inert gas canister, or to activate an inert gas fire suppression system even without starting a fire. Of course, all this can be activated remotely.

So, the next time you need a character killed in one of your stories, you might consider placing that character in a room or vault that can be sealed off rapidly before the character can escape and then remotely activate the fire suppression system or attach a gas canister to flood that area with one of these inert gases.

The cause of death will be asphyxiation (suffocation/oxygen-depletion) but without an obvious source and with no external evidence of trauma or foul play.

Thoughts? Comments? I’d like to hear them!

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