PREVENT OR ADEQUATELY CONTROL EXPOSURE

APPLYING THE IDEAS

Aluminium powder clearly possess several properties which make it a hazardous substance for anyone exposed to it. For this reason, it becomes necessary to consider how to limit or control that exposure.

Prevention of exposure to any hazardous substances is the ideal objective in any workplace process. It could be achieved by either:

• Replacing hazardous substances used in a process with those that are not hazardous or are safer to use, or
  

• Modifying the process so that hazardous substances are no longer required or produced as waste products or residues
  

However, for many processes, these approaches aimed at complete prevention of exposure to a hazardous substance are simply not possible. For example, the cost of completely removing exposure to a hazardous substance might be so high as to make a process economically non-viable. In these cases exposure must be controlled to the extent that any risk to health is deemed to be insignificant or the exposure is below levels defined in legislation. Control of exposure can be achieved through the following approaches:

• By completely enclosing the process and hazardous substances within it (Highest Priority)
  

• By partially enclosing the process and hazardous substances and providing local exhaust ventilation (LEV)
  

• By using general instead of local exhaust ventilation
  

• By adopting methods which reduce the likelihood of accidental or incidental spillage or leakage of hazardous substances
  

• By reducing the duration of exposure to hazardous substances
  

• By providing personal protective equipment (Lowest Priority)
  

The placing of provision of personal protective equipment (PPE) at the bottom of the list of priorities is entirely deliberate since it avoids the use of PPE as the sole means of reducing exposure to dangerous materials which are best controlled by other means. Of course, there is no reason why PPE cannot also be used with higher priority control measures if this further reduces the likelihood of exposure, for example, through accidental spillage or release.

So, once adopted, how do you know when the control of exposure is adequate? For many substances advice on control is given in the material safety data sheet (MSDS). So, providing you are using the substance for the intended use and that advice on control methods is adopted, exposure is normally regarded as being adequately controlled. In the final analysis, however, it will only be by measurement or monitoring of the amount (level) of exposure to the hazardous substance that adequacy of control can be determined. 

So what does this all mean for our process?

Can aluminium powder be replaced by a less hazardous substance?
The short answer is yes. There are several other powders or techniques that can be applied to the development of latent fingerprints on smooth, non-porous surfaces. However, our crime scene examiner is confident that aluminium powder is more effective than alternative powders in developing latent marks, and since it is vital to recover marks as effectively and with the best detail as possible, the use of aluminium powder is considered necessary.

Can the process be modified to minimise exposure to the powder?
Our crime scene examiner is highly skilled in using the powder, and has attended courses to maintain best practice, and knows that a combination of Zephyr brush works best with this powder. Other brushes which do not disperse the powder into the air quite so much are available, but they are not so equally effective in developing detailed fingerprints. Since this latter aim is of paramount importance, this idea is rejected.

It is recognised that where possible, it is sometimes better to remove an item from the scene to the fingerprint development laboratory where processes can be carried out in controlled and clean laboratory conditions. This approach would completely remove any likelihood of exposure at the scene. However, it is not always possible or practical to have items developed away from the scene, and anyway, local force policy is to develop marks at the scene, if possible. In this "volume crime" scenario, our crime scene examiner is developing marks on window and door frames, and so there can be no question about modifying the process.

Can the process be completely or partially contained?
It is neither practical nor economically viable to contain areas of this type of scene when working within it, and because the scene examiner is skilled in using aluminium powder, the scene is examined "as is".

Can local or general exhaust ventillation be made available?
Yes it can. It should be possible to use a portable extractor to evacuate the air space in the region in which the examiner is working. Such extraction could take the form of a filtered exhaust system (rather like a vacuum cleaner) with a receiving nozel close to the surface being dusted, although in some instances, this is not particularly practical. Where possible, this would surely have the effect of removing the dust from the airspace, minimising formation of dust clouds, and reducing the amount available for inhallation by the examiner.

Use of such such a device might introduce new potential hazards not the least of which might include static or electric discharge, not to mention the possible physical risks to the examiner in placement of the extractor in not-so-easy-to-access places. Nevertheless, a small extractor cabinet could quite easily be used in the treatment of small portable items at the scene.

Can accidental spillage of aluminium powder be avoided?
We are all human and accidents do happen, so one cannot completely remove the possibility of spillage of the powder. The amounts of powder used at any instant are always small (a small jar rather than a large tub) and so  spillage, whilst possible, and its effects, are minimised.

Can the duration of exposure be reduced?
The time taken to treat a given surface by our scene examiner is always kept to a minimum. In any event,  the degree of exposure through inhallation should be limited to the maximum permissble exposure limit (over an 8 hour period). The MSDS gives this value as 4 mg/m³ for the total respirable dust.

Can personal protective equipment be used?
Yes it can, and should be used. Face mask, disposable scene suit and gloves, and goggles where deemed appropriate. The question then becomes "which particlar mask should be used?"

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