banner rfu
clean air clean water

Winds of Warning: Chlorine Dioxide Spill

Watershed Sentinel, December 1994

People in British Columbia often refer to the sulphur-laden aroma of the province’s pulp mills as “the smell of money.” But in one mill town in October 1994, the smell of chlorine bleach held a whiff of the stench of death.

By Delores Broten

At 1:10 in the morning of October 17, 1994, the MacMillan Bloedel pulp mill at Powell River experienced the worst chlorine accident in BC history. The top thirty feet of the wood stave vat storing final bleached pulp collapsed. Hurled projectiles ruptured two adjacent chlorine dioxide tanks, spilling 600,000 litres of chlorine dioxide, which was eventually pumped into the ocean. There were no human fatalities from the spill.

Chlorine dioxide is a highly toxic, corrosive and unpredictable gas. It is ten times more toxic than chlorine and can kill by lung damage at 5 parts per million. It has a nasty tendency to spontaneously combust in solutions higher than 10%.It is too dangerous to transport, so pulp mills manufacture it on site. It is a new chemical introduced in the pulp and paper industry, introduced despite the fears of workers because, unlike chlorine, it does not form dioxins during the bleaching of wood fibres.

The chlorine dioxide gas, slowly rising from the spilled liquid, was the real danger to the workers and residents of Powell River and Sliammon Reserve, the First nation village 3 kilometres up the road. The Workers’ Compensation Board has commended MB staff on their quick actions to contain the crisis, especially the kraft operating crew who stayed to shut down the plant. However, WCB’s investigation notes that one or more workers were observed in the “hot zone” without respirators.

Slow to Tell Town

MB officials were slow to notify the neighbours. According to the Vancouver Sun, although the Emergency Officer phoned the Provincial Emergency Program within one hour of when the spill occurred, the tapes prove that there was no mention of chlorine dioxide, just spilled pulp, even though the gas was drifting around the evacuated mill in visible yellow-green clouds. The fire department in Powell River was finally alerted by Sliammon at four o’clock in the morning.

MB continues to reassure the residents of the townsite in Powell River that they were never in any danger, because the gas was blowing out to sea. The Canadian Coast Guard warned all boats to stay 1.6 kilometres offshore for the ensuing two days.


To date, the BC Ministry of Environment (MOE) , which is still investigating, says that there is little evidence of long-term environmental damage. However, because of the gas, MOE officials were only allowed on the water to test environmental impact on Wednesday morning, two days after the accident. A consulting firm which does regular monitoring for the mill will investigate further, under designs laid out by BC Environment.

Biologists do not expect any bioaccumulative or contaminating impact from the clean, but deadly, chlorine dioxide, which was heavily mixed with water. No pulp effluent, acids, resins, or organochlorines were released with the chlorine dioxide, although a lot of the spilled pulp fibres did get washed into the ocean.

Only a swathe of destruction where a stream of liquid chlorine dioxide overflowed the berm and spilled over the railway track into the mouth of the Powell River testifies to the seriousness of the spill. MOE Assistant Regional Manager Ray Robbe in Surray estimates that about 25% of the liquid took this path.

Few Options

When faced with the reality of spill, MB had only three options for disposal. A chemical called sodium thiosulphate will neutralize chlorine dioxide, but only 1,000 lbs. was immediately available, while at least 5,000 lbs was required. A second option, pumping the liquid gas up to the secondary treatment tanks where the “bugs” would breadk it down, was started, but discontinued at the orders of the Powell River Public Health Officer when air monitoring showed a “spike of .07 ppm,” according to Steve Hodges, environmental officer for MB. The only remaining option was to pump the spill out into Malaspina Strait through one of the regular underwater diffusion outlets of the mill.

The mill was eventually fined $100,000 for the spill. All kraft mills in British Columbia continue to use and store chlorine dioxide on site.

The mill will release the results of its internal investigation in early December. Norm Bush, manager of the mill, told the Watershed Sentinel that the wood and bands around the bottom of the tank had recently been replaced.


Bush said that the future of the mill was in jeopardy because of the provincial laws to eliminate the discharge of organochlorines and because of the fibre shortage. However, since the mill has rights to power and water from Powell Lake, Bush concluded that, “There’ll probably always be a mill here, but who knows what kind?”




Back to Top