purifying respirators are acceptable. Let’s return to the situation above were 2.69µg of fentanyl was suspended in the air. If all of that material was in the respiratory zone and it were fentanyl, an N95 mask would be sufficient. But, what if it were carfentanil? Now, we are approaching the analgesic dose and a N100 would be more suitable. What if the purity of the material was 10% or 100%, versus 3%?
Recommendations for respiratory protection As you can see, as the incident risk level escalates, the requirement for a minimum of a N100 respirator becomes clear. The results of the calculations above support the current recommendations set forth by the US InterAgency Board6
and the National
Institute for Occupational Safety and Health7
(NIOSH), both of whom
recommend the N100/P100/R100 filtering facepiece respirator as a minimum level of protection.
Risk analysis for dermal protection It is important to understand the skin’s substructure in order to appreciate how fentanyl permeates the skin. In its simplest form, skin comprises three layers, the epidermis (outermost), dermis (centre), and the hypodermis (inner). Many factors such as size and solubility in both the lipid (epidermis) and aqueous (dermis) layers of the skin affect a material’s ability to penetrate the skin. Fentanyl is sufficiently small and is able to rapidly diffuse into the lipophilic epidermis due to its high lipid solubility, with the free base diffusing the fastest. Because fentanyl’s water solubility is less than its lipid solubility, a ‘depot’ of fentanyl forms at the junction between the epidermis and the dermis. The time profile for a fentanyl patch, which has the added benefit of ethanol in its matrix to increase absorption, is one to two hours before detectable amounts are found in the
respiratory tract and mucous membranes were protected) and then wait another hour before reaching the lethal dose. This is not operationally viable in an emergency response context. If, however, a 5cm2
area of
the skin on the palm of the hand was covered in fentanyl for 15 minutes, an estimated 75ng of fentanyl would be able to penetrate and reach the blood stream after about one to two hours. This is well below the 2.5µg required to exhibit symptoms in an average person. Therefore, while skin absorption is not a high-risk entry route by which responders would be adversely affected, opportunities for direct or indirect skin contact should be minimised as any skin absorbed opioid will contribute to the overall total dose received. The pharmaceutical industry study
referenced earlier reported an average of 30µg of fentanyl was deposited under the protective equipment used by operators during non-bulk operations with the highest areas of exposure being at the hands, arms, and neck. They were wearing disposable Tyvek coveralls, boot covers, nitrile gloves, and full-face air-purifying respirators. They found deposition occurred over the entire body, but the highest levels were at the interface regions of the protective ensemble (hands, arms, and neck). The Tyvek clothing also showed a residual contamination level on the outside of the garment of 800ng/cm2
.4 For exposed tissue lacking the
epidermis, such as mucosa (eyes, nose, and mouth), allow for a 30-fold increase in the rate of fentanyl absorption,8
therefore, it is imperative
that the eyes, nose and mouth are always protected. In addition to the recommended respiratory protection, goggles, preferably indirectly vented ones, should be employed unless a full- face respirator is used.
blood serum, 12-16 hours to reach a therapeutic level, and 36 hours to reach the maximum serum concentration.8 In order to reach a lethal dose (2.5
mg) of fentanyl via the skin, calculations show that a subject would need to cover their entire body (approximately 17,000cm2
) with pure
fentanyl and leave it there for longer than two hours (provided the
What does this mean? It tells us that we must select appropriate protective equipment for the task and ensure it is donned and used correctly. It also tells us we should decontaminate and doff correctly to avoid any further contamination.
Recommended protective clothing For the reasons cited above, and the varied tasks and operational environments we encounter, it is recommended that particulate tight protective clothing be employed when dealing with milling lab operations to minimise exposure at interfaces and permeation of particles through the
www.cbrneworld.com CBRNe Convergence, Orlando, USA, 6-8 November 2018
www.cbrneworld.com/convergence2018
February 2018 CBRNe WORLD
37
CBRNeWORLD
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