|
 Safety, Environment
& Security |
 |
 |
 |
| WEBSITES |
|
|
| |
Back to SSG 2
Photo: Joachim Sjöström
Harmless cargo that kills
Insufficiently ventilated spaces with hazardous vapours and low concentration of oxygen are highly dangerous. In Sweden alone, seven persons have lost their lives during a period of only two years and several were seriously injured.
Globally, there have been recent reports from oil and chemical tankers where seafarers have died when entering nitrogen inerted tanks. The accidents in Sweden, however, happened while handling seemingly less dangerous cargo such as fish and wood products like pellets, chips and unbarked timber. It could well be considered a fairly harmless cargo if it was not for the biological and chemical processes that inescapably and unnoticed take place in the hold. Different gases like carbon monoxide, carbon dioxide and hydrogen sulphide are produced and the oxygen in the air is either consumed or displaced.
After the fatal accident on board the Saga Spray in November 2006, when one seafarer lost his life and seven others were injured, a research project was initiated to learn more about the risks. Urban Svedberg, PhD at the department of occupational medicine at Sundsvall Hospital, is an expert on emissions from storage of wood pellets. He is part of the Swedish and Canadian research team that have measured and analyzed the atmosphere in cargo holds on nine different ships. The preliminary result presented in December last year showed scaring results.
“The highest recorded level of carbon monoxide was over 13,000 ppm”, says Urban Svedberg.
Alarming result
This is alarming in several ways. To start with, the level is significantly higher than the 35 ppm that is the limit for workers according to Swedish law. At 10,000 ppm, or one per cent of carbon monoxide in the air, the natural content of oxygen and nitrogen in the air is replaced. When measuring the oxygen level the result can still show around 20 per cent and thus wrongly give the impression that the area is safe to enter. In fact, unconsciousness and death occur within a few minutes. In this case it is vital to check the air for hazardous gases as well as checking the oxygen level. When carbon monoxide is present in air with low oxygen content the atmosphere is even more dangerous and 2,000–3,000 ppm can be lethal.
“It is important to measure the atmosphere before entering”, says Urban Svedberg, but adds that the makers have a challenge in developing the instruments.
The mining industry is known for its use of canary birds to indicate harmful gases. In British mining pits the yellow feathered detectors were in service until 1986, when they retired in favour of more advanced systems. But there is still room for technology improvements. Today, there is no hand-held instrument that can measure over 1,000 ppm carbon monoxide and a potential fixed gas warning system would need to be both exact in the low range and still manage a high gas concentration of up to 15,000 ppm.
Any enclosed area onboard, be it a tank, chain box, cargo hold or a stair casing, must always be ventilated before entering. This is often done by simply opening a manhole or a cover hatch. But according to Urban Svedberg, this is not enough.
“It must be done by mechanical ventilation to get sufficient airing”, says Urban Svedberg and points out an additional risk:
“An open door can be inviting and easy to enter without taking necessary precautions and depending on where the warning sign is placed, it is not always possible to see the sign in an open position.”
Urban Svedberg recommends a combination of routines, mechanical ventilation and constraints to come to terms with the risks.
Rigorous routines and procedures dictate who is allowed to enter and under what conditions, working alone should not be permitted and it is vital to establish routines for communication and have equipment for rescue.
“Mechanical ventilation should be built in from the start”, says Urban Svedberg and hopes that naval architects understand the risks and where possible develop fixed systems for ventilation for the ships that are built today.
It is important that the fresh air is not taken from the cargo hold and preferably has both feed and suction fans. The ventilation must not be started during the voyage, since this involves a risk of fire.
A physical constraint like a grating or similar should be placed and locked over an open manhole or stair casing to prevent someone entering without taking necessary precautions.
A typical accident is when someone is just going in to fetch or check something and enters because it is so close, both in distance and time needed.
Protective equipment
A final resource is always personal protective equipment and it should be used whenever there is any doubt about the air quality. It is important that everybody realises that an ordinary filter mask with dust or gas filter is not enough. A breathing apparatus is the only thing that protects against lack of oxygen.
“It is important not to rely solely on rules and organisation for safety”, says Urban Svedberg and compares with other industries like aviation and power plants, where the safety to a large extent emanates from technological systems.
“This might be especially important in shipping, where the manpower is mobile and sometimes poorly educated, implying problems reading and understanding instructions in a second language.”
Seven people dead in only two years and in Sweden only proves that this is a safety issue to take seriously. You may not get a second chance.
//Cecilia Österman
Latest update 14-02-2008 10:30
|
|
 CURRENT SSG |
|
No 18/2008
Order a copy
|
 |
| CURRENT SST |
|
No 19/2008
Köp numret
|
|
|
2008