At first the US (predictably) denied that WP had been used but were later forced to reverse this position.
But so what if they did? You may ask.
The use of white phosphorus on the battlefield is not new, or indeed always intended to harm. Nor is it banned by any treaty to which the US is a signatory. There are three ways in which WP may officially be used: It is used in flares to illuminate the battlefield, it is used to generate dense smoke-screens to mask troop movements - especially in urban environments - and it is also used in particularly unpleasant incendiary bombs. More detailed descriptions of these uses can be found at GlobalSecurity.org.
None of these uses appears to meet the definition of a 'chemical weapon'.
It is the least obvious of these uses, however, which is most likely to be the problem: the smoke-screen. Though it seems unlikely that an army would deploy an obscurant which was acutely harmful to their own troops, here is what GlobalSecurity.org has to say about it:
Medical personnel should be prepared to treat potential reactions to military smokes once such smokes have been introduced to the battlefield. Exposure to heavy smoke concentrations for extended periods (particularly if near the source of emission) may cause illness or even death. Casualties from WP smoke have not occurred in combat operations.So far, not much worse than walking to the Neasden branch of Ikea down the North Circular. Bear in mind, however, that it would be illegal to pump car exhaust into an enemy installation, as it contains a toxic gas.
White phosphorus fume can cause severe eye irritation with blepharospasm, photophobia, and lacrimation. Irritation of the eyes and irritation of the mucous membranes are the most commonly seen injuries. These complaints remit spontaneously with the soldier's removal from the exposure site. The WP smoke irritates the eyes and nose in moderate concentrations. With intense exposures, a very explosive cough may occur, which renders gas mask adjustment difficult. There are no reported deaths resulting from exposure to phosphorus smokes.
Phosphorus smoke is composed of particles or droplets of phosphorus pentoxide, upon the subject of which Oxford University's website has this to say:
StabilityNot the same story really.
Stable, but reacts violently with water, alcohols, metals, sodium, potassium, ammonia, oxidizing agents, HF, peroxides, magnesium, strong bases.
Toxic and may be fatal if inhaled, swallowed or absorbed through the skin. Very destructive of mucous membranes. Eye contact may lead to serious permanent eye damage. Corrosive - causes burns.
So what is the difference between the relatively benign fog of war and whatever it was that charred away the lips, noses and eyes of the women and children of Fallujah? The answer is proximity and concentration. There is a big difference between running through a drifting veil of stinging smoke in the open and cowering, terrified, in a basement while artillery pounds the street outside and a WP round goes of in your living room. Remove yourself from that exposure site if you can.
If you doubt, then you can always experiment with having a barbeque indoors next summer*.
While the US military continues to maintain that it does not use chemical weapons it is clear that this is merely a legal argument and not a rational one. At its least severe, WP smoke has deleterious effects very similar to tear gas or other choking agents which are classified as chemical weapons. As an area-effect weapon - which it is, whether intentionally or not - it does not discriminate between civilians and combatants (lawful or otherwise).
Other clues as to the uses of WP can be gleaned from between the lines of "The Fight for Fallujah," in the March-April 2005 issue of Field Artillery magazine:
WP proved to be an effective and versatile munition. We used it for screening missions at two breeches and, later in the fight, as a potent psychological weapon against the insurgents in trench lines and spider holes when we could not get effects on them with HE. We fired “shake and bake” missions at the insurgents, using WP to flush them out and HE to take them out.
While I profess no battlefield expertise, I invite you to try to imagine how a fighter ensconced in a redoubt proof against the direct and indirect effects of an high explosive barrage might be 'flushed out' by WP rounds. If he cannot be reached by the blast and shrapnel of the HE, then what difference does the phosphorus make that would cause him to prefer to die by other means?
It can only be the smoke.
Leaving aside the ommission of WP smoke from the schedules of the Chemical Weapons Convention, the following is clear:
If the US Military fired phosphorus munitions into Fallujah, then they indubitably used chemical weapons against civilians.
*Only don't, because it would be very stupid.