A 20-strong international team of engineers, chemists and paramedics leave the Netherlands for Syria on Monday to embark on the most hazardous mission in the history of disarmament: to dismantle one of the world's biggest chemical weapons arsenals, during a civil war, under extreme deadline pressure.

In 95-degree heat, inspectors from the international Organisation for the Prohibition of Chemical Weapons (OPCW) will wear body armor and helmets over their chemical protection suits, sometimes carrying air tanks on their backs, in their efforts to abide by a UN security council resolution to destroy about 1,000 tons of nerve agents such as sarin and other poisonous gases such as sulfur mustard.

Syria's President Bashar al-Assad vowed to co-operate with the mission in an interview with Italy's RAI News 24 TV. "Of course we have to comply [with the UN resolution]. This is our history to comply with every treaty we sign," he said.

The inspectors are due to arrive in Damascus on Tuesday and meet Syrian officials the day. They will need to work quickly to meet the tight deadlines agreed by the security council on Friday.

In the first few days, a group of 20 inspectors drawn from about a dozen countries will have to fill the gaps in Syria's initial disclosure of its inventory of poison gases, nerve agents, delivery systems and production sites and fine tune the logistics for visiting the declared sites.

At that point, some of the documentation and political liaison specialists in the team will leave, and other experts will arrive, including chemical engineers, analytical chemists and medical specialists in case of accidental contamination. Within days the reinforced contingent will be split into field teams that will fan out to the declared weapons sites and laboratories. The inspectors will not say how many locations are involved as the Syrian declaration was confidential, but it is believed there are about 25 on the list.

Their first priority will be the locations where the weapons are produced. Under the UN resolution, all chemical production and mixing plants, as well as equipment used for filling rockets and shells with nerve agents or sulfur mustard gas, must be destroyed by 1 November, so as to crush the heart of the program as quickly as possible. But to get the job done in time, the Syrians – with international oversight – will have to use some rough and ready methods.

"We could fill reactors with concrete, perhaps, or they could smash them up if they're particularly delicate – if they're glass-lined reactors for example. Or equipment can be destroyed with explosives or by having a tank drive over it," said one senior OPCW official involved in the planning of the operation.

The official stressed that everything would be done in partnership with Syrian technicians: "We'll identify, in conjunction with our Syrian colleagues, critical pieces of equipment and then invite them to destroy them," he said. "The whole process will be conducted in a collaborative manner. It's not as if we turn up and point at something and say: blow that up; drive that over that equipment; fill that with concrete."

He said that the Syrian government had co-operated so far: the organisation submitted its initial list of inspectors to Damascus on Friday and got approval the next day, with no objections to any team members on the basis of nationality.

"We have already seen from dealings with them there is a willingness and an engagement to do this," the official said. "They have made a strategic decision."

The provisional plan is to concentrate the Syrian arsenal in a couple of major sites where mobile chemical neutralization plants and incinerators can be used to destroy it. Russian and US intelligence analysts have said that much of the stockpile is in the form of precursor chemicals, or chemical ingredients, which are easier and quicker to destroy than pre-mixed and weaponized chemical weapons.

The deadline for destroying the whole arsenal has been set at mid-2014. Whether or not this is feasible or not will depend on the ebb and flow of the war, analysts say.

The Syrian government has reportedly consolidated its chemical weapons in roughly two dozen sites to stop them falling into the hands of rebels, but some of those sites are close to the front lines.

"The Syrian disclosure has identified a number of locations," the official said. "Some are in areas completely controlled by the Syrian government. Others are in areas that are close to confrontation lines, but some may require us having to drive through opposition territory."

To cross the lines, inspectors will rely on UN officials based in Syria who have contacts with most parties in the conflict to negotiate safe passage. The same approach was taken when inspectors investigated the large-scale attack in eastern Damascus in August, which triggered a threat of US-led air strikes and ultimately the Assad regime's agreement to disarm.

The method was far from fail-safe. A UN vehicle came under sniper fire as it crossed the lines, but there are no plans at present to bring in foreign troops to protect the inspectors. That would be a decision for the UN, which is playing a facilitating role for the mission.

Some of the members of the initial inspection team are ex-military munitions experts who have had experience of combat zones, but the fighting across shifting front lines adds an extra layer of danger to an already hazardous task, and another physical burden.

"We will have protective suits and hand-held monitors for self-protection," the senior inspector said, adding: "Doing that kind of activity while wearing body armor and helmets is not ideal. It is really at the top end of the scale of physical burden and stress and contamination control. Wearing protective suits and body armor is physiologically pretty hard."

The risks of being in or near the front line of a civil war, in 95-degree heat, while trying to secure toxic chemicals, will give the team no shortage of dilemmas: "At that point, we start to look into what's more hazardous: the guys going down with heat exhaustion, the guys being exposed to toxic agents or the guys being shot at," the official concluded.

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