Historical Note: Due to semi-recent changes in MSE guidance, the Engineering.SE community is revisiting this question
The following is the original, accepted answer based upon earlier MSE guidance.
No, we don't need one.
The StackExchange Terms of Service already cover it.
- Warranty disclaimer
To the fullest extent allowed by law, Stack Exchange disclaims any liability or responsibility for the accuracy, reliability, availability, completeness, legality or operability of the material or services provided on this Network. By using this Network, you acknowledge that Stack Exchange is not responsible or liable for any harm resulting from (1) use of the Network; (2) downloading information contained on the Network including but not limited to downloads of content posted by subscribers;
and
- Limitation of liability
In no event shall Stack Exchange, its directors, officers, shareholders, employees, members, agents, consultants, contractors, partners, vendors and service providers (including, without limitation, hosting and telecommunications providers) be liable with respect to the Network or the Services for (a) any indirect, incidental, punitive, or consequential damages of any kind whatsoever;
And this has been hashed out a few times over on Meta.Stackexchange. I particularly like Shog's opening logic within his answer.
In my experience, giving folks who are already prone to arguing semantics more words to (mis-)interpret doesn't tend to lead anywhere good.
Individual contribution
Individuals are already protected with a disclaimer of liability through the Terms of Service. Emphasis added from previous quote of Section 9.
- Limitation of liability
In no event shall Stack Exchange, its directors, officers, shareholders, employees, members, agents, consultants, contractors, partners, vendors and service providers (including, without limitation, hosting and telecommunications providers) be liable with respect to the Network or the Services for (a) any indirect, incidental, punitive, or consequential damages of any kind whatsoever;
Past-precedent:
Some sites, such as Mi Yodeya, have had disclaimers prominently focused on their site. See this meta.SE question for a screenshot of what it used to look like. However, that has since been removed.
This historical M.SE question shows a request for the disclaimer, and Atwood's response. I point this question out because that disclaimer is no longer on Mi Yodeya.
Additional Meta StackExchange references
Not surprisingly, this subject has been discussed a lot by the network. The answer that keeps coming back is that the Terms of Service already cover the disclaimer.
"But we're different!"1
To an extent, this is true. Licensed, professional engineers exist and many countries have laws regulating the practice of Engineering. But Engineering isn't the only field that's regulated. Medicine, Finance, and Law, are other fields that are regulated.
Questions pertaining to those disciplines regularly come up on other Stack Exchange sites that do not have their own disclaimers. Insisting on Engineering.SE being different and that it needs to have its own disclaimer potentially sets a precedent that implies other aspects of the StackExchange Terms of Service not applying to this site.
I think that's a bad precedent to set, and I don't believe Engineering.SE needs a disclaimer.
1 Being engineers, yes, yes indeed we're different. But that's not really relevant to this question. :-)