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Drain Opener - Chlorine Gas Exposure

Hydrochloric Acid




Areas of Expertise

Michael Fox, PhD.



Drain Opener - Chlorine Gas Exposure

Police and medics responded to a 911 call made by an elderly gentleman concerning odor. When they arrived they found the man down in the kitchen. First responders were unable to enter and treat the man immediately due to the strong odor of bleach, which was later determined to be chlorine gas. The gentleman was pronounced dead that day.

According to the report of the Fire Captain they had found 6 bottles of a liquid alkaline drain opener and 1 bottle of an acid drain opener. The Captain's report does not indicate whether all of the bottles were empty. However, some photographs were taken. One photo showed at least 3 empty bottles of the alkaline drain opener in a wastebasket. Another photo showed one bottle of the alkaline drain opener and one bottle of the acid drain opener next to the bathroom toilet.

The alkaline drain opener was an alkaline solution of about 5-10% sodium hypochlorite (NaOCl) while the acid drain opener is a solution of 10-20 % hydrochloric acid (HCl). The chemical reaction between the two drain openers is represented by the following equation:

2HCl + NaOCl Cl2+ H2O + NaCl

From the photograph of the two drain openers next to the toilet, it appeared that they were indeed mixed together.

Assuming that the alkaline drain opener contains 10% NaOCl and that it was added to an excess of HCl contained in the acid drain opener, approximately 2.8 moles of chlorine gas (Cl2) would be liberated. At Standard Temperature and Pressure (STP) this would equal 62.7 liters or 2.2 cubic feet of chlorine gas. If that amount of chlorine gas were diluted to 1 part per million by volume (ppm), it would occupy a volume of 2.2 million cubic feet.

According to The Chlorine Institute, the following is a list of chlorine exposure thresholds reported for human exposure:

0.2-0.4 ppm
Odor Threshold
1-3 ppm
Mild, mucous membrane irritation
5-15 ppm
Moderate irritation of respiratory tract
30 ppm
Immediate chest pain, vomiting, dyspnea, cough
40-60 ppm
Toxic pneumonitis and pulmonary edema
430 ppm
Lethal over 30 minutes
1000 ppm
Fatal in a few minutes

A 2000 square foot home with 8 ft ceilings would have 16,000 cubic feet of volume. That would correspond to about 137-ppm chlorine gas assuming the conversion of one complete bottle of the alkaline drain opener to Cl2. This would explain why the first responders could not enter the home.

If the Cl2 generated were initially confined to a smaller room, such as a bathroom of about 1000 cubic feet in volume, the initial concentration of Cl2 could be 2,200-ppm, which would explain the lethal effect on the elderly gentleman. Of course, he fled the bathroom to get to the kitchen to call 911, but clearly he could have easily been exposed to a lethal dose of 1000-ppm. It is understood from the police report that while the man was able to make the 911 call, he was not able to speak clearly. Therefore, the Cl2 gas had already seriously affected him.

Given that it would take a substantial amount of acid to neutralize the alkalinity of the alkaline drain opener and that there were no other sources of acid reported at the scene of the incident, it is more likely than not that the acid drain opener (in scene photos) was the source of acid involved in the release of the chlorine gas. The release of chlorine gas (Cl2) from an alkaline solution of sodium hypochlorite (NaOCl) requires acid and the acid drain opener (HCl) was the only available source of acid reported.

Chemaxx was asked to explain the chemistry involved in mixing the two drain openers together and to determine the most likely source of the acid needed for the reaction. The case settled before trial.

Dr. Fox is an explosion expert, fire expert, and chemical expert with extensive experience in OSHA chemical regulations and chemical safety.