Iraq sarin shell is not part of a secret cache

In the mid-1980s I served as the intelligence officer for a Marine artillery battalion. Stationed in Twentynine Palms, Calif., I would often find myself deployed in the field, on exercises where thousands of live artillery rounds were fired downrange.

In keeping with the Marine artillery motto of "shoot, move, communicate," we were always moving from one firing location to another to simulate modern war. This mobility had us often passing through live-fire impact areas. One thing you quickly learned was not to touch anything lying on the ground, because modern artillery shells had a high "dud" rate, meaning they didn't always function the way they were intended. Tens of thousands of these "duds" were scattered across the desert terrain, not unlike those found in Iraq.

What makes this relevant now is the ongoing speculation about the source of the sarin chemical artillery shell that the US military found rigged as an improvised explosive device (IED) last week in Baghdad. If the 155-mm shell was a "dud" fired long ago - which is highly likely - then it would not be evidence of the secret stockpile of weapons of mass destruction (WMD) that the Bush administration used as justification to invade Iraq.As a United Nations weapons inspector in Iraq from 1991 to 1998, I know that the Iraq Survey Group (ISG), the US-led unit now responsible for investigating WMD in Iraq, could quite easily determine whether this shell had been fired long ago or not. Given the trouble the administration has had in documenting its past allegations about WMD, releasing the news of last week's sarin shell without the key information about the state of the shell itself seems disingenuous.

As a former UN inspector, I'm also familiar with the level of disarmament achieved concerning Iraq's banned WMD. And during my time in Iraq, 95 percent of the WMD produced by Iraq were verifiably accounted for. But I've always contended that Iraq is a WMD archaeological site, and that if one digs long enough, vestiges of these past WMD programs will be uncovered. Determining whether the discovery of the sarin artillery shell represents such an archaeological discovery, or is part of Saddam Hussein's alleged stockpile of WMD, rests with a full forensic exam of the shell.

The key to whether the sarin artillery round came from an arms cache or was a derelict dud rests in the physical characteristics of the shell. The artillery shells in question were fitted with two aluminum cannisters separated by a rupture disk. The two precursor chemicals for the kind of sarin associated with this shell were stored separately in these containers. The thrust of the shell being fired was designed to cause the liquid in the forward cannister to press back and break the rupture disk, whereupon the rotation of the shell as it headed downrange would mix the two precursors together, creating sarin. Upon impact with the ground - or in the air, if a timed fuse was used - a burster charge would break the shell, releasing the sarin gas.

Many things go wrong when firing an artillery round: the propellent charge can be faulty, resulting in a round that doesn't reach its target; the fuse can malfunction, preventing the burster charge from going off, leaving the round intact; the rupture disk can fail to burst, keeping precursor chemicals from combining. The fuse could break off on impact, leaving the fuse cavity empty. To the untrained eye, the artillery shell, if found in this state, would look weathered, but unfired.

What gives away whether the shell had been fired is the base-bleed charge, which unlike the rest of the shell, will show evidence of being fired (or not). Iraq declared that it had produced 170 of these base-bleed sarin artillery shells as part of a research and development program that never led to production. Ten of these shells were tested using inert fill - oil and colored water. Ten others were tested in simulated firing using the sarin precursors. And 150 of these shells, filled with sarin precursors, were live-fired at an artillery range south of Baghdad. A 10 percent dud rate among artillery shells isn't unheard of - and even greater percentages can occur. So there's a good possibility that at least 15 of these sarin artillery shells failed and lie forgotten in the Iraq desert, waiting to be picked up by any unsuspecting insurgent looking for raw material from which to construct an IED.

Given what's known about sarin shells, the US could be expected to offer a careful recital of the data with news of the shell. But facts that should have accompanied the story - the type of shell, its condition, whether it had been fired previously, and the age and viability of the sarin and precursor chemicals - were absent. And that's opened the door to irresponsible speculation that the shell was part of a live WMD stockpile. The data - available to the ISG - would put this development in proper perspective - allowing responsible discussion of the event and its possible ramifications.

Given that the US is in the midst of a contentious presidential campaign, it's essential that accurate data about Iraq be available to the electorate. The handling of the sarin shell incident is the greatest justification yet for shutting down the ISG, and the immediate return to Iraq of UN weapons inspectors - if for no other reason than to restore a vestige of credibility to a disarmament effort that long ago lost its moral compass.

• Scott Ritter was a UN weapons inspector in Iraq (1991-1998) and is author of 'Frontier Justice: Weapons of Mass Destruction and the Bushwhacking of America.'