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There is not rule as to how much profit or loss will trigger an audit.  What your accountant is probably referring to is I.R.C. Section 183, which disallows any net loss from an activity conducted without a bonafide profit motive.  There is no single factor that is determinative, the regulations set forth nine factors the IRS will typically consider to determine whether a taxpayer has a profit motive.  According to the IRS:

You must generally consider these factors in determining whether an activity is a business engaged in making a profit:

• Whether you carry on the activity in a businesslike manner and maintain complete and accurate books and records.
• Whether you have personal motives in carrying on the activity.
• Whether the time and effort you put into the activity indicate you intend to make it profitable.
• Whether you depend on income from the activity for your livelihood.
• Whether your losses are due to circumstances beyond your control (or are normal in the startup phase of your type of business).
• Whether you or your advisors have the knowledge needed to carry on the activity as a successful business.
• Whether you were successful in making a profit in similar activities in the past.
• Whether the activity makes a profit in some years and how much profit it makes.
• Whether you can expect to make a future profit from the appreciation of the assets used in the activity.

You may find more information on this topic in section 1.183-2(b) of the Federal Tax Regulations.

In addition, under the regulation, a profit motive is presumed when the activity has shown a profit in 3 of of the last 5 years.  If the presumption applies, the IRS has the burden of showing there was no profit motive by using the nine factors above.  If the presumption does not apply, the taxpayer has the burden of showing there was a profit motive.  

So, if your single member LLC is a legitimate business with a profit motive, you don't have anything to worry about, even if it has a loss for the fourth year in a row.